What does the acronym SETI stand for, a field Sagan championed?

SETI stands for Search for Extraterrestrial Intelligence, the scientific effort to detect evidence of intelligent life beyond Earth. Researchers commonly look for artificial patterns in radio waves, optical signals, or other possible technological signatures.

The modern field grew rapidly after the development of radio astronomy. In 1960, astronomer Frank Drake conducted Project Ozma, an early experiment that monitored nearby stars for radio transmissions. Carl Sagan became one of SETI's best-known public champions and helped connect the search with planetary science, astronomy, and questions about humanity's place in the universe.

SETI is often confused with attempts to send messages to aliens. Traditional SETI mainly listens for signals; active efforts to transmit messages are usually called METI, or Messaging Extraterrestrial Intelligence. Despite decades of searches, scientists have not confirmed a signal from an extraterrestrial civilization. The acronym refers to the field itself, not to a particular telescope or organization.