What does presumption mean?

If you presume something (i.e., if you believe that something is true based on likelihood or probability), then that belief is a presumption. For example, believing that your favorite baseball team is going to win the championship because they have won the last two in a row is a presumption.

“Presumption” can also mean “audacious attitude or conduct” (e.g., “His presumption in taking the CEO’s parking spot was met with disbelief”).