Base unit (measurement)

A base unit (also referred to as a fundamental unit) is a unit adopted for measurement of a base quantity. A base quantity is one of a conventionally chosen subset of physical quantities, where no quantity in the subset can be expressed in terms of the others. The SI units, or Systeme International d'unites which consists of the metre, kilogram, second, ampere, Kelvin, mole and candela are base units.In the International System of Units, there are seven base units: kilogram, metre, candela, second, ampere, kelvin, and mole.A set of fundamental dimensions of physical quantity is a minimal set of units such that every physical quantity can be expressed in terms of this set. The traditional fundamental dimensions of physical quantity are mass, length, time, charge, and temperature, but in principle, other fundamental quantities could be used. Electric current could be used instead of charge or speed could be used instead of length. Some physicists have not recognized temperature as a fundamental dimension of physical quantity since it simply expresses the energy per particle per degree of freedom which can be expressed in terms of energy (or mass, length, and time). In addition, some physicists recognize electric charge as a separate fundamental dimension of physical quantity, even if it has been expressed in terms of mass, length, and time in unit systems such as the electrostatic cgs system. There are also physicists who have cast doubt on the very existence of incompatible fundamental quantities.