What is "Echo"?

Echo

A sound impulse arising from a reflection with such a strength and time delay after the direct sound that it is perceived as a repetition of it. A distinct echo is heard if the delay between the direct sound and the reflected sound is >50 ms. Echos can either be created naturally as described above. However, they can also be created electronically as an effect applied to music productions.

Shorter delays are more likely to be experienced as a coloration of the direct sound.