Other forms: importances
Importance is the state of being greatly significant. If you're invited to your cousin's wedding and your friend's circus-themed birthday party on the same day, you'll have to decide which event has more importance to you.
Something or someone that is particularly notable can also be referred to with the noun importance. The historic and symbolic importance of the "Declaration of Independence" means that most kids learn about it in history class. In your history class, you'll also learn about the people who had positions of importance in drafting the "Declaration," like John Adams and Thomas Jefferson.