IK - Inverse Kinematics
Inverse kinematics isn’t a focus on getting the end effector, rather it’s about having the end effector and finding a configuration for the joint system so that it will reach said end effector from the origin.
IK can be quite difficult and resource intensive. Furthermore, most explanations regarding inverse kinematics are filled with Robotics jargon which may make it somewhat difficult for the average user to pick up.
So what does all this mean to in simple terms? It means one can place an connected object such as bone or endpoint, then all of the bones above the object automatically rotate into position. It's a big advantage when a character has to reach for something.
An additional bonus to using an underlying skeleton is that the bones and joints provide a natural control structure for deforming the surface. With deformation, individual control points on the geometry are moved in relation to the bones and joints.
When a model is "skinned" or "enveloped" over a skeleton, either Inverse or Forward Kinematics can be used to animate it. There are still benefits to using Forward Kinematics on some parts of your skeleton. Some packages allow the use of both Forward and Inverse Kinematics on the same skeletal chain and even allow you to switch between them on the fly. Others allow you to switch only with great effort on your part. To do this, you usually have to employ constraints (think of constraints as magnetic forces that can be keyframed on and off), expressions (mathematical formulas), or a combination of both.Refer 
- Use the arrow key to move the bunney obj and watch an simple connected arms uses IK to reach the end point.
External Links :
- Character Animation: Skeletons and Inverse Kinematics
- IK Slides WRT to motion
- IK Slides
- IK Motion captures and Graphs
Source On GitHub (Coming Soon)