MANIPULATION.
Robots which must work in the real world require some way to manipulate objects; pick up, modify, destroy or otherwise have an effect. Thus the 'hands' of a robot are often referred to as end effectors, while the arm is referred to as a manipulator. Most robot arms have replacable effectors, each allowing them to perform some small range of tasks. Some have a fixed manipulator which cannot be replaced, while a few have one very general purpose manipulator, for example a humanoid hand.

Grippers:

A common effector is the gripper. Usually it consists of just two fingers which can open and close to pick up and let go of a range of small objects.
Vacuum Grippers: Pick and place robots for electronic components and for large objects like car windscreens, will often use very simple vacuum grippers. These are very simple, but can hold very large loads, and pick up any object with a smooth surface to suck on to.

General purpose effectors:

Some advanced robots are beginning to use fully humanoid hands, like the Shadow Hand (right), or the Schunk hand. These highly dexterous manipulators, with as many as 20 degrees of freedom and hundreds of tactile sensors can be difficult to control. The computer must consider a great deal of information, and decide on the best way to manipulate an object from many possibilities.