Water Hole
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In SETI, the Water Hole is the band of radio frequencies between 1420 MHz and 1640 MHz. This is the band between the hydrogen line and the strongest hydroxyl spectral line, and is notable because it is a quiet region between two notable frequencies; it is theorized that this would be a good band for communications to or from extraterrestrial intelligences.
The term was coined by Bernard Oliver. The combination of hydrogen and hydroxyl yields water (the "water" part of the name); the "hole" part refers to the sudden drop in radio noise within this band. The term also serves as a pun as it has been theorised that extraterrestrial species would use this band as a commonly recognised communication channel (in English a watering hole is a vernacular reference to a common place to meet and talk).
Several SETI programs, including SETI@home search in the Water Hole.
