What does a colon represent in math?

Answer 1

The two main uses are:

To indicate a ratio - particularly of 3 or more quantities. Whereas with two quantities, a ratio may be written as 3:4 or 3/4, only the first form is used for more quantities. For example, "a triangle with sides in the ratio 5:12:13 is right angled".

Another use is as a separator, in the sexagesimal (base 60) system - similar to the decimal point. For example in hours, minutes and seconds as in 9:30 am or 19:45:32.