The colon is the symbol ":". It is used in a number of different ways in mathematics.
1. To denote ratio or odds, as in 2:1 (voiced "two to one").
2. To mean such that in constructions such as (voiced "the set of numbers such that ).
3. To give a name to a map, e.g., (which is equivalent to the function notation ).
4. As a part of the symbol sometimes used to mean " is defined as ."
5. To delineate the three elements of trilinear coordinates, i.e., .
6. To indicate an extension field degree of an extension field , denoted .
7. To denote colon product of two dyads.