What is a variable pump rifle?

The Daisy model 880 and the Crosman

760 are both Variable pump rifles. To charge the rifle you must pump the forearm from 1 to 10 times to store enough air to fire the pellet or BB. With each pump you store a little more air in the air cylinder and increase the power of the rifle when it is fired. It takes a minimum of 2 pumps to store enough energy/air to make the BB or Pellet fire. Never pump the rifle more than 10 times or

it may rupture the seals.