You'll almost certainly have heard about coronavirus - it's the reason schools were closed to most pupils across the UK and why people are being asked to stay at home if they can and maintain social distancing measures when they go out.
It's been the main news story for months, with the government holding daily briefings to keep everyone updated with what is going on.
Coronavirus is a new flu-like virus spreading around the world. The virus causes an illness called Covid-19, though lots of people still refer to the illness as 'coronavirus' as that is how it was known at first.
Prime Minister Boris Johnson announced new rules in March which meant people could only leave home for essential shopping, or to care for someone elderly or vulnerable.
Even schools were closed to all children except those of key workers and those who needed special help.
People were told they could leave the house to exercise but only once a day and away from other people if they do not live in the same house.
Only shops selling really important things like food, medicine and home maintenance items were allowed to stay open - the rest were told to shut. People have been calling this a "lockdown".
Lockdown measures were also introduced by leaders in Scotland, Wales and Northern Ireland.
The lockdown rules are being reviewed every three weeks and each country has been gradually relaxing the rules since May.
For example, people from different households can now meet, as long as they keep up social distancing, while some school pupils in England have been allowed back to class.
Many shops have reopened in England, Northern Ireland and Wales, with Scotland doing the same from Monday, 29 June - and certain people in England can also form 'support bubbles'.
It means adults who live alone, and single parents with children under 18, can 'team up' with one other household - visit each others' homes, spend time indoors together and stay overnight.
Lots of big sporting and music events have been postponed - including the Olympics and Paralympics, the Euro 2020 football tournament which was due to take place this summer, and the Glastonbury festival - to avoid the risk of the virus spreading in crowds.
Football across the UK was stopped for several months but in June Premier League football restarted.
Crowds aren't allowed to attend. with games taking place behind closed doors.
Lockdown measures are being gradually eased in each country and each of the UK nations have been setting out their own steps for the relaxing of the lockdown, to let people know when things might start to return to normal.
However, that all depends on the number of infections continuing to fall.
A new alert system was launched in May to help tell people how the country is dealing with the pandemic and how high the rate of infection is.
The alert system has five levels, with five being the worst, meaning lots of people being infected, and one being the best, with no cases of coronavirus. Some changes are being allowed because we are moving to lower alert levels, the government says. The UK moved from level four to level three on 19 June.
Adults who cannot work from home have been allowed back to work in England, where schools are also returning - although the government has changed its mind about getting all primary school children back to class before the summer holidays.
Wales is planning for some children to go back on 29 June, but Scotland and Northern Ireland say children there will return after the summer holidays.
Each country has also set up a system to try to track who may have coronavirus and to alert other people they might have been in contact with.
Successful track and trace systems will help to control the the virus and will also help to tell the people in charge when it's safe to ease restrictions.
Experts including the UK's chief medical adviser, Professor Chris Whitty, and Sir Patrick Vallance, the UK's chief scientific adviser, have been giving regular updates to explain why the actions they are taking can help tackle coronavirus.
Prof Whitty has said some sort of social distancing is likely to go on until a vaccine or medicines to help treat Covid-19 are available, which could take until next year.
People showing symptoms of coronavirus have been told to self-isolate - which means staying at home and avoiding contact with anyone else.
The UK government says you must do this for seven days, although other countries say it should be 14 days. Anyone who lives in the same house as someone with these symptoms should also stay at home for 14 days.
From 8 June, all people arriving in the UK have been told to self-isolate for 14 days under new rules.
Those arriving by plane, ferry or train - including UK nationals - have to provide an address where they will self-isolate and face fines of up to £1,000 if they do not follow the rules.
Anyone arriving from the Republic of Ireland, the Channel Islands or the Isle of Man does not have to complete the form or enter quarantine. Workers in some industries such as road haulage and medical professionals, who are providing essential care, can enter the UK as normal without self-isolating.
Other advice people are being told to follow is to only use the NHS (National Health Service) - that means going to hospital or the doctors - when it's absolutely necessary. People should dial 111 rather than going to their doctor or to an NHS hospital. If it's an emergency, you must still call 999.
It is now compulsory for people in England and Scotland to wear "face coverings" on public transport.
Official guidance in Wales and Northern Ireland is that face coverings should be worn on public transport or in places like shops where social distancing isn't possible, though it is not yet compulsory there.
The WHO says medical masks only need to be worn by people with symptoms or by carers or medical professionals looking after people with Covid-19, though it updated its guidance in early June to say face coverings in busy areas could be helpful.
As of 25 June there had been more than nine million cases of coronavirus in 188 countries around the world. While most people recover, many people have died.
About a quarter of the total number of cases around the world have been in America , while large numbers of infections have been recorded in Brazil and India - where cases are still rising - and Russia.
The UK, Italy, France and Spain have been the worst-hit European countries. It's been estimated that about 4.5 billion people - more than half the world's population - have had to live with social distancing measures.
Lockdown measures are being slowly lifted in phases across most parts of the world. Shops are reopening and many children are back in school - although lots of places are insisting that people wear masks in public places and keep social distancing in place.
A pandemic is a disease that spreads in a number of countries around the world at the same time.
The first cases were identified in Wuhan, a city in China. It is thought it might have come from bats at a wildlife market there.
The coronavirus is a respiratory virus - that means it affects people's breathing and lungs. Like the cold and flu bugs we get in the UK, it can spread from person to person by coughing, or contact with contaminated surfaces or skin.
It can lead to more serious illnesses like pneumonia. This is dangerous for vulnerable people, such as the very old or people who are weaker due to other illnesses.
The disease has been linked to a large number of deaths in the UK, and health officials say that most of these were elderly people, or people who already had other health issues. Symptoms include fever, a cough, and a loss of smell or taste.
Because it is a new virus, there's currently no vaccine or medicine available yet to treat it - although lots of scientists around the world are working hard to develop one.
The UK government is investing in a vaccine that is currently being developed at the University of Oxford - tests are already being carried out on people to see how they react to it.
However, there is a chance it might not work, or it could take around 18 months for it to be ready because it will have to be tested to make sure it is safe to use. Until then, the only way to prevent it spreading is to limit physical contact with people who have the virus.
Doctors says properly washing your hands is one of the best ways to help reduce the spread of the virus.
Lots of money is being spent by different governments to find out more about the virus too - knowing more about it increases the chances of being able to deal with it.
Scientists are also trying out existing drugs to see if they can help treat people who become unwell.
Testing is important because it can help the government track cases and make sure they are looking after those who are ill, and stopping them passing it on to others. The countries with the most success in tackling the virus have all had effective testing and tracing measures.
It's also really important for key workers. That's because even if they have shown mild symptoms, like a cough or high temperature, if a test shows they don't have the virus they can keep on working.
On 18 May it was announced that anyone in the UK over the age of five who has symptoms is also allowed to get a test.