Power trio. Stripped-down drummer-bassist-guitarist format that experienced a mid-to-late ’60s vogue (Cream, the Jimi Hendrix Experience, Blue Cheer, Mountain) thanks to new amplifier technology and a blues-purist revolt against psychedelic fussiness, both of which obviated the need for a rhythm guitarist. Which was all well and good until Rush came along and managed to make even power trios sound noodly and PROG-ish.