This was a Thursday night block of "adult" animated shows that debuted on Spike in 2003, right when the network changed its name from "TNN." The creation of the block was apparently inspired by the success of Cartoon Network's adult swim programming block, but The Strip only lasted one season. The only show I ever watched in this block was Gary the Rat, but it also included shows called Stripperella and Ren & Stimpy "Adult Party Cartoon". (And also I guess some reruns of the original Ren & Stimpy Show, which had originally run on Nickelodeon.)
Note: This is not to be confused with "Late Night Strip," an unrelated late night programming block that debuted on Spike in 2006. I've never seen any of that, and I'm sure I'd have no interest in it.