B♭7sus4 (also written A♯7sus4) is a dominant seventh suspended fourth chord made of 4 notes: B♭, E♭, F, A♭. It sounds a dominant chord that hangs before it settles, and you hear it in funk, gospel and the moment before a 7th chord. It is the V chord of E♭ major and turns up in 2 other keys.
The library above opens on B♭7sus4 with 14 shapes up and down the neck. Tap a shape to hear it, or play it one string at a time.