There were a few attempts to describe ski resorts in OSM, all with more or less success. So I commit this proposal: site=piste.
You are more than welcome to comment or ammend it here: discussion.
For those not used to relations, it’s just a way to relate various elements(way, nodes, piste routes) with each other, here by a simple thing: ski !
The main practical goal of this is to give these site a name, so that we can easily find winter_sport areas as such in the database.