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.
As it is the purest form of American music, and since all rock, rap, r&b, some jazz, and pop groups are influenced by the blues whether they try to or not, I'd say it is popular everywhere.