what do they mean by non inline since c++17 ???

Declaration of a non-inline(since C++17) static data member inside a class definition:

struct S
{
    int n;               // defines S::n
    static int i;        // declares, but does not define S::i
    inline static int x; // defines S::x
};                       // defines S

int S::i;                // defines S::i

what do they mean by non inline since c++17 ???

source : https://cppreference.com/cpp/language/definition
do they mean inline variables are available since c++17 or what exactly ? i don't get it