1. n. The tendency of young animals to follow the first moving thing they see. In the wild, this is usually the mother, but in captivity, where the mother may not be the first thing they see, they might follow a human being or any moving object. Source: Durrell, G. and L. Durrell. 'A Practical Guide for the Amateur Naturalist'. Alfred A. Knopf, New York, 1989.
2. n. A kind of associative learning in which an animal rapidly learns during a particular critical period to recognize an object, individual, or location in the absense of overt reward; distinguished from most other associative learning in that it is retained indefinitely, being difficult or impossible to reverse. Source: Keeton, W.T. and J.L. Gould. 'Biological Science (4th Edition)'. W.W. Norton & Co Ltd. New York. 1986.