The phrase "huge fan" is an idiomatic expression used to describe someone who has a great deal of admiration, enthusiasm or affection for something or someone. In other words, it means that this person is very much in love with, enjoys and supports the object of their fandom wholeheartedly. A huge fan may be passionate about sports team, musician, actor/actress, book series, video game, etc., and they often showcase their admiration through various forms such as attending events or concerts, collecting memorabilia, dressing up in costumes, participating in online forums, creating artwork, writing fanfiction, etc.