User blog comment:ReverseZoom101/2 Weird things you may or may not have noticed in The Flash/@comment-27700324-20161019153635/@comment-7890302-20161019211149

Actually, fanservice can be two different things.

One is 'Hey look, that babe is wearing a bikini!'

Or, fanservice can be 'Hey, the movie is using that sword that was barely in the book, but everyone loves!'

Fanservice is basically anything that makes a fan of the series feeled serviced. Whatever from sexy, or well loved surprises from an old thing.