Lit. "now go screw like bunnies, we expect you to create 15 Jews over the next 20 years. Go!" Source: YIVO.

one of the things frum people say when folks get engaged or married. It is also the most frequently written phrase on Onlysimchas.com besides for “omg I am sooooooooooooooooo happy for you channie”

as in, "They should be zoche to build a Bayis Ne'eman B'yisroel." (Obligatory last sentence of every sheva brachos speech.)