Dissipation is a term that is often used to describe ways in which energy is wasted. Any energy that is not transferred to useful energy stores is said to be wasted because it is lost to the surroundings.
Electrical cables warming up are a good example of this. It is not useful to have warm wires behind a television as energy is dissipated to the surrounding air.
In a mechanical system, energy is dissipated when two surfaces rub together. Work is done against friction which causes heating of the two surfaces - so the internal (thermal) energy of the surfaces increases. Adding lubricant between the surfaces reduces this friction and so less heat is wasted, like the inside of a car engine.
Recently, LED light bulbs have been introduced to replace filament lamps, as they are much more efficient. Using these causes less energy to be wasted as heat.
Energy is usually lost by heating up the surroundings though sometimes energy is dissipated as sound.
The ways in which energy is dissipated depends on the system: