(statistics, broadly) A quantity whose value is random and to which a probability distribution is assigned, such as the possible outcome of a roll of a dice.

(mathematics, statistics) The value of a variable minus its mean, divided by its standard deviation.

(logic) A variable that can either be true or false.

(statistics) A nominal variable.

(statistics) A variable that has a continuous distribution function, such as temperature.

(statistics) A variable that takes values from a finite or countable set, such as the number of legs of an animal.

(statistics) A random variable that is not an independent variable and may bear any effect on the behaviour of the subject being studied.

(statistics) An extraneous variable in a statistical model that correlates (positively or negatively) with both the dependent variable and the independent variable.

(programming) A variable whose value is stored directly in a register for faster access.

(systems theory) A variable that describes the state of a dynamical system.