Short form = Stan.
1. Suburban, usually Caucasian adolescent Eminem fanboys.
2. Known to predictably declare Eminem to be "the greatest rapper alive" despite that they usually don't listen to rap to bother to substantiate this claim.
3. A reference to "Stan," the title and main character of one of Eminem's songs off the "Marshall Mathers LP" about an obsessive fan who imitates Mathers' look, writes incoherent and disturbing fan letters, and eventually kills his pregnant girlfriend and himself because Eminem didn't reply in time.
4. Best visually exemplified in the music video for "The Real Slim Shady," also from the "MM LP." Throughout the video, Eminem is surrounded by a legion of white guys wearing the signature white Tees and jeans and the signature bleached haircut, nodding rhythmically to the song; thus achieving an effective Village of the Damned vibe to the video.
Stanleys don't actually listen to rap, but are instead "hip-hop fans' " equivalent to otaku/Wapanese "Japanese culture enthusiasts" (see fanboy).
They don't *really* know anything about the subject of their obsessive fandom, but do everything in their power to nevertheless fail to convince you that they do.