From Podpedia

A Humblehug is a term coined by Brady in H.I. #96: The Humblehug to refer to a half handshake, half hug.

The maneuver consists of shaking the hand of another while touching mirrored shoulders and using the other hand to clap the other participant on the back. Sometimes compared to a chest bump.[1]

Not to be confused with the Parkour High Five Hand Grab.