- A number that is raised to a power, or base of an exponential function. This finds common use, for example, in the depiction of numbers, for instance, 10 is the base used in the decimal system, whereas 2 is the base in the binary system. See also numeral system and radix
- The base of a logarithmic function.
- One of the parallel sides of a trapezoid or the unequal side of an isosceles triangle.
- In topology, a base (topology) for a topology is a set of open sets such that every element of the topology is a union of the base sets. See also subbase.
- Base of a transform in mathematics
- In biochemistry, see nitrogenous base.
- In baseball, a base is one of 4 bags placed at corners of the infield diamond that a player has to run to after hitting the ball.
- In a transistor the base is the controlling connection to the junction.
- In Marxism describes the material equipment and material relations of human society, as distinct from the 'superstructural' forms of society - laws, customs, ideas, beliefs, etc.
- BASE jumping is a popular variation on skydiving.
- The name of the terrorist group Al-Qaida translates as "the base."
- In 2001, the catchphrase "All your base are belong to us" swept across the Internet.
- In chemistry, a base is the reactive complement to an acid. (Sometimes the term alkali has been used historically where base is now preferred.) See Acid-base reaction theories. Technically, a substance capable of neutralizing acid, with a pH greater than 7.0. See Table of bases
- Base is also an isolated settlement in inhospitable conditions that must rely on outide help in order to survive, such as military base, Antarctica base, Moon base.