`std::optional` is a feature in the C++ programming language that allows developers to represent an optional value. It can either contain a value of a specified type or indicate that no value is present. This is useful for functions that may not always return a valid result, helping to avoid the use of special sentinel values or pointers. By using `std::optional`, programmers can write clearer and safer code. It provides methods to check if a value exists and to access the value if it does. This helps prevent errors related to uninitialized variables and enhances code readability and maintainability.