What: Strength building pushing movement for the chest - with new standards implemented by the US Army and as a choice for the USAF.
How: With hips locked straight and head neutral, lower chest to ground, pick up hands off the ground, extend them out to the side until your elbows are locked out. Bring them back to center, and complete a push up - maintaining a straight back, "plank" position. 

This video is from the US Air Foce on the form required for it's PFT, and is the same form/standards used by the US Army for the ACFT.