The `typeid` operator in C++ is used to obtain the type information of an expression at runtime. It returns a reference to a `std::type_info` object, which contains details about the type, such as its name. This is particularly useful in scenarios involving polymorphism, where the actual type of an object may not be known at compile time. When using `typeid`, it is important to note that it works differently for polymorphic and non-polymorphic types. For polymorphic types, `typeid` will return the dynamic type of the object, while for non-polymorphic types, it returns the static type. This feature helps developers understand the actual types being used in their programs.