a ] Kinematic link ( or element ) :
It is defined as a resistant body which has relative motion with some other element. e.g. crank, Piston, cylinder, frame
b] Kinematic pair :
When two links are connected in such a manner that relative motion between them take place in a definite way then it is called kinematic pair.
c] Kinematic chain :
When two or more kinematic pairs are joined together, they form kinematic chain.
d] Mechanism :
If one link of a kinematic chain is fixed it is called mechanism.
e] Inversion :
When different links of a kinematic chain are fixed we get different mechanisms, these mechanisms are called inversions of that kinematic chain. The number of inversions of a kinematic chain are equal to number of links in that chain.