The expression "x - 3" represents a simple algebraic equation where x is a variable that can take on different numerical values. The "- 3" indicates that 3 is being subtracted from whatever value x represents. This expression is often used in mathematics to illustrate how changing the value of x affects the overall result. For example, if x equals 5, then "x - 3" would equal 2, since 5 minus 3 equals 2. This type of expression is fundamental in algebra and helps in solving equations, graphing functions, and understanding relationships between numbers.