A conditional statement in programming is a feature that allows the execution of different code segments based on whether a specified condition is met (true) or not met (false). The most common conditional statements are 'if', 'else if', and 'else'. They are used to perform decision-making operations in a program, like executing a specific block of code only if a certain variable meets a particular criterion. Conditionals are fundamental in controlling the flow of a program, enabling it to respond differently to varying inputs or states.