Infinity -- from Wolfram MathWorld

Infinity, most often denoted as infty, is an unbounded quantity that is greater than every real number. The symbol infty had been used as an alternative to M (1000) in Roman numerals until 1655, when John Wallis suggested it be used instead for infinity. Infinity is a very tricky concept to work with, as evidenced by some of the counterintuitive results that follow from Georg Cantor's treatment of infinite sets. Informally, 1/infty=0, a statement that can be made rigorous using the limit...