in addition to the usual things or the usual amount:
They need to offer something extra to attract customers.
one/a few etc extra
I got a few extra in case anyone else decides to come.
I'll be making $400 extra a month.
2 [+ adjective/adverb]
used to emphasize an adjective or adverb:
You're going to have to work extra hard to pass the exam.
an extra special effort