What does « the ID » of a diamond or a gemstone mean ?

What does « the ID » of a diamond or a gemstone mean ?

The ID of a diamond or a colour gemstone is defined with the certificate that comes with it, done by commercially independent gemmology laboratory. MASSILIA-DIAMANT welcomes its clients to consult the pages “Learn more/Description of a gemstone certificate” and ”Learn more/Description of a diamond certificate” on its website.