There’s an iD preset that sets this tag (it’s not just auto completion from Taginfo): id-tagging-schema/data/presets/piste/piste.json at main · openstreetmap/id-tagging-schema · GitHub
The preset is called “Snowsports Trail/Piste”.
Just wanted to point this out - I don’t map winter sports so I can’t tell you who uses it or why.