Mucosal melanotic macule https://en.wikipedia.org/wiki/Oral_pigmentation#Melanotic_macule
Mucosal melanotic macule in mucosa labii, palati et gingivae oralis inveniri potest. Mucosal melanotic macule laesiones pigmentatae benignae sunt, quae in cavitate oris inveniuntur, ex incremento pigmentationis epithelii et laminae propria. Typice, area est fusca, nigra, caerulea vel grisea, bene circumscripta; laesiones plerumque minus quam 10 mm diametro, sed in quibusdam casibus maiores esse possunt. Est morbus benignus.

Diagnostica et curatio
Valde benigna, si uniformis in figura et colore.

Informationes plurimae ― Latine
References Black and Brown: Non-neoplastic Pigmentation of the Oral Mucosa 30671761 
NIH
Addison’s Disease (Hypoadrenocorticism),Peutz–Jeghers Syndrome,Laugier–Hunziker Syndrome (Idiopathic Lenticular Mucocutaneous Pigmentation),Drug-Related Discolorations,Melanotic Macule,Melanoacanthoma,Smoker’s Melanosis,Amalgam Tattoo/Foreign Body Tattoo,Black Hairy Tongue