Osaekomi-waza (Pinning techniques) is one of the groups of Katame-waza (Grappling techniques). These pins represent different types of hold down techniques when holds another one on his back. 

Here is the list of all Pinning Techniques (Osaikomi-waza):

Also check out Choking Techniques (Shimewaza) and Joint Locking Techniques (Kansetsuwaza).

Or vist animation Throwing Techniques (Nagewaza) page.