The aerobatic loop has to be the most common aerobatic manouver and is one of the most basic. You will see hundreds of these manouvers at an air show, and I would be surprised if you don't!
A vertical circle entered from straight and erect level flight. A positive pitching movement is used at all points in the loop to draw the circle, so that the aeroplane canopy is pointing inwards. Both the inside and outside loop are sometimes casually referred to as a 'loop the loop'.