Type checking is a process used in programming languages to ensure that variables and expressions are used consistently with their defined data types. This helps prevent errors by verifying that operations are performed on compatible types, such as adding two numbers or concatenating two strings. Type checking can be done at different stages, including during compilation (static type checking) or at runtime (dynamic type checking). In statically typed languages like Java or C++, type checking occurs before the program runs, allowing developers to catch type-related errors early. Conversely, dynamically typed languages like Python perform type checking while the program is executing, which can offer more flexibility but may lead to runtime errors if types are mismatched.