I am certain this piece is Native American, and I believe Southwest pueblo, with the lower half of the black clay body polished to a sheen and showing some minimal decoration. What makes it unusual, and quite special I think, is the folded over and finger pinched/thumb pressed neck, which contributes (along with the wear to the exterior and view of the interior) to me thinking this is a very old (pre-columbian) piece. What I really love is the visceral-ness of that finger pressing--the mark of one specific person many hundreds of years ago, I believe, leaving a lasting impression, literally, in the clay. A humble, utilitarian pot in some senses, but also quite a singular one. 

 4 1/4" t x 4 1/4" widest diameter.  Good, presumed very old condition, with some surface wear/perhaps some loss of decoration to the lower half. No chips or cracks or other issues at all.