An element is one of two or more individual mesh objects (that is, groups of contiguous faces) grouped together into one larger object. For example, if you attach one box to another, you create one mesh object from the two boxes. Each box is now an element of the object. Any function you perform on that object affects all its elements. However, you can manipulate the elements independently at the Element sub-object level.
The antler is one element of the moose head.