riding vs trail riding

riding and trail riding both are nouns.

Word	Noun	Adjective	Verb	Adverb
riding	Yes	No	No	No
trail riding	Yes	No	No	No

As nouns, trail riding is a hyponym of riding; that is, trail riding is a word with a more specific, narrower meaning than riding:

Other hyponyms of riding include bronco busting, endurance riding, pack riding.

riding (noun)	trail riding (noun)
travel by being carried on horseback	riding along a roughly blazed path
the sport of sitting on the back of a horse while controlling its movements