An "if statement" is a fundamental programming construct that allows a program to make decisions based on certain conditions. It evaluates a condition, and if that condition is true, it executes a specific block of code. For example, in the programming language Python, an if statement can check if a variable is greater than a certain value and perform actions accordingly. If statements can also include "else" and "elif" (short for "else if") clauses to handle multiple conditions. This enables more complex decision-making processes. For instance, a program can check if a number is positive, negative, or zero, executing different code blocks for each case.