It's called the dolphin pose.

From all fours, place your forearms on the ground, shoulder distance apart. Next, tuck your toes, and lift your hips into dolphin, which is downward facing dog on your forearms.

Then do 10 "dolphin pushups". Look forward and reach your chin toward your thumbs, coming almost to a forearm plank. Use your exhale to lift your hips back into dolphin pose, raising hips back toward the ceiling. That’s one rep.

If you don't have access to weights doing this 10 times every day will tone up your arms really nicely. Dolphin pose is a shoulder, neck and trap opener that works your core in addition to your arms.