A closed interval is a range of numbers that includes both its endpoints. It is typically represented in mathematical notation as [a, b], where a and b are the lower and upper bounds, respectively. This means that all numbers between a and b, including a and b themselves, are part of the interval. Closed intervals are commonly used in mathematics, particularly in calculus and analysis, to define domains for functions and to describe sets of solutions. They differ from open intervals, which do not include their endpoints, denoted as (a, b). Understanding closed intervals is essential for studying concepts like limits and continuity in mathematics.