IK is the opposite of FK, forward kinematics. In FK, you move and rotate bones in order to make movement. For an arm (eg), you rotate the shoulder, the arm, the forearm, then the hand, to maybe get your character to hold something.
In IK, you'd start with the hand using an IK target, and move up from there if necessary.
Hobby animator: IK is a lifesaver!
Noob animator: IK?
A person who is so selfish that they only think of themselves and will not help anyone even if they need medical help or are starving to death.
The word comes from the Ik tribe in Africa in Uganda written about in the book "The mountain people". The people of the Ik tribe live a very selfish lifestyle where it is every person for themselves.
It has been said by some that the people of the modern world are becoming like the Ik tribe. And thus the word Ik.