The act of cunnilingus preformed post bars but pre-sex. A play on the word 'foreplay' and the popular Taco Bell ad campaign '4th meal.' This has other hidden puns such as insinuating you would be eating a taco late at night.
Guy 1: I saw you buying drinks for Lisa all night, did you end up hooking up with her.
Guy 2: Yeah, after a 4th meal.