Sailing Glossary - Term Degree day

Generally, a measure of the departure of the mean daily temperature from a given standard; one degree day for each degree (°C or °F) of departure above (or below) the standard during one day. Degree days are accumulated over a \season.\"" As used by the U.S. Army Corps of Engineers, degree days are computed above and below 32°F, positive if above and negative if below. ""