The terms Nordic skiing and cross-country skiing are often used interchangeably, but there are some differences between the two. Nordic skiing is a term that refers to a group of skiing disciplines that originated in Scandinavia, including cross-country skiing, ski jumping, and Nordic combined (a combination of cross-country skiing and ski jumping). In this sense, Nordic skiing is a broader term that encompasses cross-country skiing as one of its disciplines.
Cross-country skiing, on the other hand, specifically refers to a type of Nordic skiing that involves skiing across flat or undulating terrain, using skis that are longer and narrower than downhill skis. Cross-country skiing can be done on groomed trails, in backcountry terrain, or on urban trails such as those used for rollerskiing.
In summary, Nordic skiing is a term that includes a range of skiing disciplines, including cross-country skiing, while cross-country skiing is a specific type of Nordic skiing that involves skiing across flat or undulating terrain using long, narrow skis.