Celsius and centigrade are two names for essentially the same temperature scale (with slight differences). The centigrade scale is divided into degrees based on dividing the temperature between which water freezes and boils into 100 equal gradients or degrees. The word centigrade comes from "centi-" for 100 and "grade" for gradients. The centigrade scale was introduced in 1744 and remained the primary scale of temperature until 1948. In 1948 the CGPM (Conference General des Poids et Measures) decided to standardize several units of measurement, including the temperature scale. Since the "grade" was in use as a unit (including the "centigrade"), a new name was chosen for the temperature scale: Celsius.

The Celsius scale remains a centigrade scale in which there are 100 degrees from the freezing point (0°C) and boiling point (100°C) of water, though the size of the degree has been more precisely defined. A degree Celsius (or a Kelvin) is what you get when divide the thermodynamic range between absolute zero and the triple point of a specific type of water into 273.16 equal parts. There is a 0.01°C difference between the triple point of water and the freezing point of water at standard pressure.