**Definition:**
A set is a collection of distinct objects, considered as an object in its own right. Sets are fundamental in mathematics and can contain numbers, letters, or other elements.

**Key ideas:**
- Sets are usually represented by curly braces, e.g., {1, 2, 3}.
- Elements in a set are unique; duplicates are not allowed.
- Sets can be finite (with a limited number of elements) or infinite (with no end).
- Operations on sets include union, intersection, and difference.

**Why this topic matters in this category:**
Understanding sets is essential for solving problems in mathematics, as they form the basis for more complex concepts and operations.