echo

ECHO may stand for:

• ECHO (European Commission), the European Community Humanitarian aid Office
• ECHO (music award), a German music award
• Echo 1 communications satellite
• Shortened Echocardiography
• Enteric Cytopathic Human Orphan virus
• ECHO Lake Aquarium and Science Center in Burlington, Vermont
• Extended Care Health Option, a supplemental insurance program for disabled dependents of U.S. uniformed service members
• ECHO IV,"Electronic Computer for Home Operation", an experimental home computer from 1966
• Gloucestershire Echo, a daily newspaper founded in 1873

The Exoplanet Characterisation Observatory (EChO) was a proposed space telescope as part of the Cosmic Vision roadmap of the European Space Agency, and competed with four other missions for the M3 slot in the programme. On February 19, 2014, the PLATO mission was selected in place of the other candidates in the programme, including EChO.

In audio signal processing and acoustics, an echo (plural echoes) is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single reflection of the sound source. The time delay is the extra distance divided by the speed of sound. The word echo derives from the Greek ἠχώ (ēchō), itself from ἦχος (ēchos), "sound". Echo in the folk story of Greek is a mountain nymph who's ability to speak was cursed, only able to repeat the last words anyone spoke to her. Animals that use echoes are cetaceans (dolphins and whales) and bats.