"Algebra: The area of mathematics related to the general properties of arithmetic. Relationships can be summarized by using variables, usually denoted by letters x, y, n, … to stand for unknown quantities, whose value(s) may be determined by solving the resulting equations."
From: "Algebra" The Concise Oxford Dictionary of Mathematics. Christopher Clapham and James Nicholson. Oxford University Press, 2005. Oxford Reference Online. Oxford University Press. Saint Mary's College of California. 5 September 2008