Tradgrass
A reference to the traditional style of western bluegrass, i.e as played by Tony Rice or Doc Watson. Used to differentiate from modern day "Newgrass" and "Jamgrass" and other variations popularized by bluegrass fusion artists, like Billy Strings.
Man, that new album dropped last night, straight tradgrass. Makes me want to practice my banjo, although I'll probably just get drunk, instead.