Fermi Paradox:The apparent contradiction between high estimates for the probability of extraterrestrial civilizations and humanity's lack of contact with or evidence for such civilizations.
SETI (Search for Extraterrestrial Intelligence): A scientific effort aimed at detecting signals from intelligent extraterrestrial sources.
Habitable Zone:The region around a star where conditions might be right for liquid water to exist on a planet's surface, potentially allowing for life as we know it.