An Elvish word probably derived from the stem kel-, meaning 'go' or 'run'. It was used by the Vala Yavanna to refer to that part of her natural realm capable of moving or escaping, as opposed to the olvar which were rooted in place. The terms kelvar and olvar, then, refer respectively to animal and plant life, and are essentially equivalent in meaning to fauna and flora.
After the awakening of the Elves, some of the kelvar were said to have been inhabited by powerful spirits. Most famous among these were the great Eagles that overlooked events in Middle-earth from their mountainous eyries.