The term "class name declaration" used in [basic.def]/2 (2.5) is not defined in the Standard. As a matter of fact, it is not even mentioned a second time in the spec. The term is informally introduced in the second example of [class.name]/2 as follows:

struct s { int a; };
void g() {
    struct s; // hide global struct s with a block-scope declaration
    s* p; // refer to local struct s
    struct s { char* p; }; // define local struct s
    struct s; // redeclaration, has no effect
}

where the two declarations struct s; above, as far as I can tell, are what the Standard refers to in [basic.def]/2 (2.5) as a "class name declaration". But these declarations are already defined in the Standard as an elaborated-type-specifier , or more specifically, as an elaborated-type-specifier that is the sole constituent of its declaration, as can be seen in the first form shown in paragraph [dcl.type.elab]/1.