Third inversion dominant 7th

For best results, this chord needs to be played in what the jazz books call "string bass" mode, or what an old guitar teacher of mine used to term "um-ching"... that is, E string first, and then the rest of the chord. That's how Jobim (Antonio Carlos, a Brazilian bossa nova type) plays it, and what's good enough for him is good enough for me.

You'll find it's a natural partner for the diminished chord shape (the B flat diminished here) and for a whole slew of shapes which hold the barre at the fifth fret.