What is a fathom used to measure?

A fathom is specifically defined as a unit of measurement for water depth, equivalent to six feet. It is primarily used in maritime contexts to assess how deep the water is, which is critical for navigation, fishing, and various marine activities. This measurement helps sailors determine whether their vessels can safely navigate through certain waters, avoiding grounding or colliding with underwater obstacles. The term originates from the Old English word 'fæðm,' meaning to embrace or encircle, relating to the span of a person's outstretched arms. In contrast, the other options pertain to different types of measurement, such as temperature, land distance, and weight, which do not apply to the use of fathoms in nautical terminology.