Aeolus451 on 19 February 2016
Actually, you're right and wrong. Fan service is anything that is done solely for the fans' enjoyment. It has a very broad definition. It's like how they made that Serenity film for the fans of the Firefly show. The film is basically fan service/a proper ending for the show. Panty shots in anime is fan service. It's not that confusing.
