The calorie is a pre-SI metric unit of energy. It was first defined by Nicolas Clément in 1824 as a unit of heat, entering French and English dictionaries between 1841 and 1867. In most fields its use is archaic, having been replaced by the SI unit of energy, the joule. However, in many countries it remains in common use as a unit of food energy.

Definitions of a calorie fall into two classes:

The gram calorie is not used in nutritional contexts. Instead, the large calorie is used. In this context calorie and kilocalorie are equivalent.

In an attempt to avoid confusion, the large calorie is sometimes written as Calorie (with a capital C). This convention, however, is not always followed, and not explained to the average person clearly (and is sometimes ambiguous, such as at the beginning of a sentence). Whether the large or small calorie is intended often must be inferred from context. When used in scientific contexts, the term calorie refers to the small calorie; it is often encountered in contexts such as bond and conformational energies in molecular modeling.

Michael Fred Phelps (born June 30, 1985) is an American swimmer who has, overall, won 16 Olympic medals—six gold and two bronze at Athens in 2004, and eight gold at Beijing in 2008, becoming the most successful athlete at both of these Olympic Games editions. In doing so he has twice equaled the record eight medals of any type at a single Olympics achieved by Soviet gymnast Alexander Dityatin at the 1980 Moscow Summer Games. His five gold medals in individual events tied the single Games record set by compatriot Eric Heiden in the 1980 Winter Olympics and equaled by Vitaly Scherbo at the 1992 Summer Games. Phelps holds the record for the most gold medals won in a single Olympics; his eight at the 2008 Beijing Games surpassed American swimmer Mark Spitz's seven-gold performance at Munich in 1972. Phelps' Olympic medal total is second only to the 18 Soviet gymnast Larisa Latynina won over three Olympics, including nine gold. Phelps also holds the all-time record for most gold Olympic medals, at 14.