This document defines fundamental concepts about sets, including: - A set is a collection of distinct objects called elements. Capital letters denote sets and lowercase denote elements. - Examples of sets include collections of vowels, numbers that satisfy equations, or groups like football players. - The empty set contains no elements. Sets can be finite and counted or infinite. - Membership, subsets, unions, intersections, and complements are defined. Venn diagrams can represent relationships between sets visually. - Basic counting rules give formulas for finding the number of elements in unions and intersections of finite sets.