Hypothermia is reduced body temperature that happens when a body dissipates more heat than it absorbs. In humans, it is defined as a body core temperature below 35.0 °C (95.0 °F).
Many passengers of the Titanic that either jumped into the water or fell into it died because of it, due to the cold water, which was reported to be somewhere around 28 degrees Fahrenheit that night, or -2 °Celsius.