Definition from Wiktionary, the free dictionary
- (uncountable) The working time outside of one's regular hours
- Workers are usually paid extra for working overtime.
- (sports, countable) An extra period of play when a contest has a tie score at the end of regulation.
- That last-second shot ties the game 99-99 and sends it to overtime!
- (uncountable) The rate of pay, usually higher, for work done outside of or in addition to regular hours.
- (extra period of play) extra time
Derived terms 
extra period in sports
pay for overtime work
overtime (not comparable)
- Exceeding regular working hours.