A phrase used by young men to define the act of sex with a female. Preferably with A: A younger girl than oneself or B: With a cougaron the prowl. Slam Pumps are usually a sexual act where there is no emotional commitment or drama the next day. Best case scenario you don't remember your partners name the next day or care, and neither does she.
"Dude, we went to the bar last night hooked up with two cougars, went back to their yacht and got slam pumps all night long!"