A mathematical expression is a combination of numbers, variables, and operators that represents a value. For example, in the expression 3x + 5, 3 is a coefficient, x is a variable, and 5 is a constant. Operators like addition (+), subtraction (-), multiplication (×), and division (÷) are used to combine these elements. Expressions can be simple, like 2 + 3, or more complex, involving multiple terms and operations. They do not include an equality sign, which distinguishes them from equations. Understanding mathematical expressions is essential for solving problems in algebra, geometry, and other areas of mathematics.