Also knownas langlauf, in German, or ski fond in French.
Cross country skiing comes in a couple of forms - classic (below) & skating. Both are charactarised by long thin skis, and require specialist boots and bindings. Cross crountry skiers often, but not always ski on a prepared track. Gradients are usually gentle, but speeds can be fast.
Cross country skiing has some summer time cousins - roller skiing and nordic walking.
We don't sell cross country ski kit, but here are some resources that may help you find what you need:
Yorkshire Dales Cross Country Ski Club - local enthusiasts with a small loan pool