of, relating to, or shaped like a triangle; having three angles; triangular. 2. Crystallography. having threefold symmetry. Origin of trigonal.
An online survey conducted in the U.S. points out that the most popular music genre in the U.S. is rock, with 40 percent of respondents choosing this option. The second and third most listened to music genres are oldies and country respectively, while hip hop/rap is favored by a smaller niche of American listeners.
The Music Genres List site covers many of the most popular styles of Rock music, including British Invasion (my personal favourite!), Hair Metal (one of my more amusing), and Rockabilly (one of the more fun genres.)