Eriisa: well i'm glad You asked, Ma'am, because i've long wondered myself but i guess i wasn't quite curious enough to actually go look it up. now i have.

evidently the simplest way to describe sprinkler system winterization is to say it's the process of removing all the water from the system's pipes so that the water doesn't freeze, expand, and crack them. and evidently there are three ways to do it, which are described in detail here.

i hope this answers Your question, Lady. it answered it better than *my* curiosity demanded it be answered...