Fan Service

Nothing to do with tennis or waiting tables it is also sadly not an information stream for fans. Originating in anime and manga fandom, fan service is when something is done excessively just to please the audience and is often sexual in nature. This translates into other fandoms very easily and wikipedia defines it as:

“Any gratuitous content included in some form of entertainment primarily to please a core group of fans”

In kpop fandom this can mean anything from semi-nudity and shower scenes to skinship, messing about or teasing the audience verbally.