short for blatant self promotion. Not necessarily the normal type of SPAM but also a more benign form of it which is used to advertise non-commercial websites. Still obnoxious to many people, especially if it's off-topic.

Typical BSP statements look like:

"Also see my homepage, it's really cool!"
"BTW, I run a site that deals with pet hamsters. Come visit me!"
"This site sucks. Come visit mine instead!"