What are Parallel Kinematic Mechanisms ?

A kinematic chain is an assemblage of linkages (usually rigid). These linkages are connected either by pins (revolute joints forming a kinematic chain called a mechanism) or bolted rigidly to the ground (forming a kinematic chain called a structure). Serial kinematic mechanisms consist of rigid links that are connected by pin joints in a serial fashion.
is a closed-loop mechanism where a moving platform is
connected to the base by at least two serial kinematics chains
(legs).