Declaration vs definition in C

Question

Consider the code:

int main(void)
{
    int a;
}

As far as I know, int a; is a definition, as it causes storage to be reserved

Answer 1

A declaration introduces an identifier and describes its type, be it a type, object, or function. A declaration is what the compiler needs to accept references to that identifier. These are declarations:

extern int bar;
extern int g(int, int);

A definition actually instantiates/implements this identifier. It's what the linker needs in order to link references to those entities. These are definitions corresponding to the above declarations:

int bar;
int g(int lhs, int rhs) {return lhs*rhs;}