imitation

1. The repetition in a second  voice or part of a theme, motif, or phrase presented by a first voice or part. The first presentation of the theme is called the antecedent, the answer is called the consequent, and is usually a different pitch from the antecedent. The antecedent usually continues while the consequent is coming in, and the consequent need not imitate the antecedent exactly, but may vary the tune slightly. 

 

2. The imitation by music of natural sounds such as bird songs , rain, thunder, etc.