Reactions (Reaction Manager) Use of one animation track to control others visually by using key positions called states. Used for animating facial rigs etc.
Wiring Use of one animation track to control others through a mathematical expression so only one object needs to be animated. Used for animating gears etc.
Inverse Kinematics (IK) Arranges all the elements of a hierarchical structure so that the child object aligns to an IK target. Used for movements like using a mouse where the mouse position defines the shape of the arm.
Forward Kinematics (FK) How a standard hierarchical structure is animated – i.e. manipulating the base object first, then each child in turn. Used for movements like hand waving where the objects move in arcs.
Skinning Defining how bones control a mesh object. The vertices of the mesh are linked to bones using weightings so that more than one bone can influence the movement of each vertex.
Rigging Building some control structure for a character or object – usually using bones, supplemented with control objects and IK solvers, and sometimes with wiring or reactions too.
Remember... the early bird might get the worm, but the second mouse always gets the cheese!