Someone who only reads the stuff. Readers read and enjoy science fiction, but they don't participate in fandom and may not even know of its existence.

Some readers are protofans who need only achieve contact to make their way into the microcosm, but many are not. Some who know about fandom are uninterested. Some readers go to Readercon or other cons, especially when an author they like will appear — they watch programming, perhaps visit the hucksters room, and then go home without interacting with fans.

A particularly avid reader, especially one with an academic bent, might be a stefnist.