To winterize is to prepare for cold weather. This can apply to any object that is susceptible to damage due to the cold, particularly water freezing damage.
For vehicles, the node preparing your car for cold weather covers the basics. Remember not to leave things in the trunk like water bottles or soda cans. I forgot a flat of 24 soda cans and they all exploded, causing me to spend a few days trying to clean the resulting spray festival.
For houses, one has to prepare the plumbing for the cold weather. Pipes must be drained, toilet tanks should be either drained or filled with recreational vehicle antifreeze, and all of the p-traps under the sinks need to have a dose of antifreeze tossed in. The pipes should be blown out and the hot water heater should be completely drained. It might be a good idea to replace the anode rod while you're at it to extend the life of the water heater.
Recreational vehicles are a combination of both the house and car winterizing process.
Iron Noder 2017