Fsus4 is a suspended fourth chord made of 3 notes: F, B♭, C. It sounds tense and hanging, as if waiting to resolve, and you hear it in the classic sus4-to-major move at the end of a phrase. It is the I chord of F major and turns up in 5 other keys.
The library above opens on Fsus4 with 14 shapes up and down the neck. Tap a shape to hear it, or play it one string at a time.