random variable

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A variable whose values are random but whose statistical distribution is known.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.
• noun statistics A measurable function from a sample space to the measurable space of possible values of the variable.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a variable quantity that is random