A linear expression is a mathematical phrase that represents a straight line when graphed. It typically consists of variables, constants, and coefficients combined using addition, subtraction, and multiplication. For example, the expression 2x + 3 is linear because it can be represented as a straight line on a coordinate plane. Linear expressions can be simplified or evaluated by substituting values for the variables. They are fundamental in algebra and are used in various applications, such as solving equations and modeling real-world situations. Understanding linear expressions is essential for progressing in mathematics and related fields.