AKA Stack Forward
Stacking in general just means that multiple routines or techniques were used in set at different times. You can stack routines, or openers, or any type of canned material in a set as long as it relates to the general conversation and nature of the interaction.
Being able to stack properly is a key skill of any artist, and comedians do this well, with material after material and proper transitions.
Stacking routines is key to structured game.