Reflection of a Sound Wave back to its source in sufficient strength and with a sufficient Time lag (at least 0.1 sec) to be separately distinguished by the human ear.
Also, in Greek mythology, mountain nymp. She incurred Hera's wrath with her chatter
and, as punishment, could only repeat the last words said by others. In
unrequited love for Narcissus, she pined away until her voice alone remained.