Factorial:
Used to find the total number of outcomes of a scenario with descending amounts of choices.  The factorial of n, represented by n !, denotes the product of decreasing positive integers beginning with n and working backwards to 1.  n! = n(n -1)(n -2)(n -3) . . .(3)(2)(1); Special Factorial: 0! = 1

Fundamental Counting Principle:
If event M can occur in m ways and is followed by event N that can occur in n ways, then event M followed by event N can occur in mn ways.

Outcome:
The result of a single trial; example-flipping a coin has two outcomes: heads or tails.

Permutation:
When different orderings are to be counted separately, i.e. the outcome, mn is not equivalent to the outcome nm.

Sample Space:
The set of all possible outcomes.

Tree Diagram:
A graphic organizer used to list all possibilities of a sequence of events in a systematic way; one method for calculating the total number of outcomes in a sample space.