something which is added to a basic product or service that improves it and often costs more:
Tinted windows and a sunroof are optional extras (=something that you can choose to have or not).
Be careful, there may be hidden extras (=additional charges which you are not told about).
It's got lots of useful little extras.
an actor in a film who does not say anything but is part of a crowd:
He started his acting career as an extra.