A missing sock, lost sock, or odd sock (primarily British English)[1][2] is a single sock in a pair of socks known or perceived to be permanently or temporarily missing. Socks are usually perceived to be lost immediately before, during, or immediately after doing laundry.
According to popular media articles regarding missing socks, people almost always report losing one sock in a pair, and hardly ever the entire pair of two socks. Various explanations or theories—some scientific or pseudo-scientific and others humorous or facetious—have been proposed to show how or why single socks go missing or are perceived to have gone missing.
The terms odd sock or mismatched sock may instead refer to the remaining "orphaned" sock in a pair where the other matching sock is missing or lost.