It means that
const inside that member function, i.e. it doesn’t alter the object.
this is a prvalue expression whose value is the address of the object for which the function is called. The type of
this in a member function of a class
X*. If the member function is declared
const, the type of
const X*. [section 9.3.2 §1]
const member function, the object for which the function is called is accessed through a
const access path; therefore, a
const member function shall not modify the object and its non-static data members.