The furlough scheme has helped pay the wages of millions of people who can't work due to the coronavirus pandemic.
The scheme pays employees placed on leave up to 80% of their salary, up to a maximum of £2,500 a month.
It is often used to support people whose jobs aren't feasible during coronavirus, but can also be used to support parents who have to look after children or those with other caring responsibilities.
Can I be furloughed to look after my children?
Schools have closed to most pupils in England, Scotland and Wales - while Northern Ireland will have an "extended period of remote learning".
Employees are eligible for furlough if they cannot work "due to caring responsibilities resulting from coronavirus". This includes childcare, the government says. However, employers are not obliged to furlough you.
Trade union umbrella body TUC says many businesses are not aware of this rule. It says employers should "do the right thing and furlough mums and dads".
Why has the scheme been extended?
When the furlough scheme was last extended, in November, it was at very short notice. This led to complaints that employers had been forced to lay off people they might have been able to keep.
If 100 or more people are being made redundant, for example, group meetings must start at least 45 days before anyone's job ends.
Letting employers know months in advance that furlough will be extended until the end of April could affect the business decisions they take for 2021.
"We know the premium businesses place on certainty, so it is right that we enable businesses to plan ahead regardless of the path the virus takes," Chancellor of the Exchequer Rishi Sunak said.
As coronavirus infections rise again, hospitality and entertainment venues have had to close in many parts of the UK during the run-up to Christmas.
This has increased the pressure for one of the hardest-hit sectors of the economy, where a significant proportion of staff are already on furlough.
Can I be placed on the furlough scheme?
The scheme pays some of the wages of people who can't do their jobs because their workplace is closed, or there is no longer enough work for them.
They may also be unable to work because they are clinically extremely vulnerable and cannot work safely, or they have caring responsibilities due to coronavirus, such as looking after children.
You can be furloughed whether you are on a full-time, part-time, agency, flexible or zero-hour contract, but you must have been on your employer's payroll before the extension was announced.
It is not necessary to have been furloughed before and you keep all your working rights, including annual and parental leave.
While you are on furlough you can take on other jobs, as long as you doesn't break the rules of your contract. You can also take part in training, or volunteer for an unconnected organisation.
Since July, employers have been able to bring back workers part-time, and furlough them for the rest. This will continue, and employers will have to pay employees' wages for the hours they work as normal.
What does furlough mean for employers?
While employees won't notice any difference in their pay packets, the scheme has become more generous for employers, who will pay less towards it.
Earlier in the year firms had to top up furloughed wages by 20%, with the government paying 60%. The state now puts in the full 80%, with the employer only covering pension and National Insurance contributions.
Employers may top up pay with the extra 20% if they want.
The scheme still applies throughout the UK.
About 10 million jobs have already been claimed for, at a cost of £43bn, by the middle of November.