Lamp is an acronym. L.A.M.P.=
Look
At
Me
Post
The term is generally used derisively by posters in a thread who feel the a fellow poster is attention-seeking. It is also occasionally used, perhaps tongue-in-cheek, in a thread title when a poster has had a pretty cool experience or interesting thought that they would like to share, even if it is tooting their own horn a bit (see my thread, linked below, about winning a chance to hang out with Andre Reed and get pregame field access at Gillette on Christmas Eve back in 2017). You'll notice that I use LAMP as a disclaimer in the thread title, indicating up front that it is, indeed, not much more than a "look at me post."