In C++, qualifying a symbol refers to resolving the symbol with the scope resolution operator, ::. Qualifying a symbol specifies to the compiler, (and other developers) what that symbol is part of. If the symbol is a class member, qualifying the symbol could be accomplished by specifying the name of the class and the symbol when referencing the symbol. If the symbol is enclosed within a namespace, qualifying a symbol could be accomplished by specifying the name of the namespace in addition to the symbol when referencing the symbol.

Resolving a symbol is necessary when a symbol (name) is used for more than one type. If the symbol is used by itself, the compiler will have no way of knowing which type the symbol is referring to, and will issue a ambiguity error. Resolving the symbol, by qualifying it with the scope resolution operator, ::, will inform the compiler of your intentions.