Primary Touhou fan: One who became interested in Touhou due to it's games. A longtime fan of shmup/arcade/retro-esque games, this person likes Touhou for it's actual gameplay, music and/or art/style. Probably has an interest in secondary works, but most likely enjoys the main games and ZUN's works more so.
Secondary Touhou fan: One who became interested in Touhou due to some offshoot (dojin works, IOSYS, fanart, 4chan...). May or may not have an interest in its main genre and more likely have not really played the games; if they did play, it's only to see what the game is like and doesn't get into it (i.e. 1CCing normal or completing extra). However, probably enjoys the side games (IaMP and SWR) and may or may not enjoy the fanworks. This is also the typical "Touhoufag."