Real Dictionary

leftover
If you say that something is a leftover from a past period of time, you mean that it has its origin there and still exists even though most other things connected to that time have disappeared.
You use leftover to describe an amount of something that remains after the rest of it has been used or eaten.
plural noun: You can refer to food that has not been eaten after a meal as leftovers.

leftover in American English
remaining unused, uneaten, etc.
something left over
adjective: being left or remaining, as an unused portion or amount
noun: food remaining uneaten at the end of a meal, esp. when saved for later use

leftover in British English
adjective: left as an unused portion or remnant
noun: an unused portion or remnant, as of material or of cooked food