The number of possible ways to choose combinations from total items is denoted using two parentheses with the variables and . The subscript is included to indicate that the expression represents combinations where order does not matter as opposed to permutations where order does matter. Typically, the notation is used in an expression like this:
In plain language, this represents the total number of combinations from choosing items from a collection of items. See permutations for where order does matter.
The combination formula describes the possible combinations of r elements out of a group of n elements where order does not matter.