What is a forearm pass bump in volleyball?

Answer 1

first you place the back of one hand into the palm of the other

while holding that, straighten your elbows and keep your arms together to create a flat surface.

then, move to get under the ball and push up with your legs

Answer 2

it would either be called a pass or a bump or you may hear people refer to it as a dig, especially if it was a pass off of a spike.