In math, infinity is a concept that refers to an endless quantity that's larger than every real number. The symbol for infinity resembles a sideways number eight. Students are introduced to the concept of infinity during or before middle school, but they usually don’t use infinity much until calculus.

### What Infinity Is

Although infinity is larger than any number in existence, it is not a real number. Unlike real numbers in which you add two numbers to produce a larger number such as 2+5 = 7, if you add infinity + 1, you get infinity. If you add infinity to infinity, you will see that infinity + infinity = infinity. Infinity is not only enormous, it is also endless. You cannot measure infinity; add any quantity to infinity, and you will always get infinity.

### Mathematical Examples

Although infinity isn’t widely applied before calculus, math has many examples of infinity. For example, the sequence of numbers -- 1, 2, 3 and so on -- extends infinitely. When you write certain fractions in decimal form, they will repeat infinitely. For example, a calculator will show that 2/3 equals 0.6666, but the row of sixes in the number 0.6666 doesn’t end after four digits. The sixes in the number 0.6666 continue as far as a calculator screen will allow; in theory, the number 0.6666 extends forever -- infinitely. In geometry, a line segment has two distinct endpoints – points A and B. A line, however, will extend infinitely in either direction.