A fork of Rural Dictionary
Occurs while engaging in sexual intercourse, the penis while inside the vagina, is at its utmost length and girth. Hence, The Full Slab.
Bro #1 "Ok so you banged that chick...how you think she's going to rate your performance to her friends?" Bro #2 "Doesn't matter, I gave her all I got, I gave her the full slab"