con·cav·i·ty 
/kɑnˈkævəti/ noun
plural con·cav·i·ties /kɑnˈkævəti/ noun 1 [noncount] : the quality or state of being concave : the quality of being curved inward
▪ the concavity of the lens 2 [count] : a shape that is curved inward : a concave shape
▪ The lower back forms a concavity. ▪ The large concavities along the wall of the restaurant are like private rooms.
▪ the concavity of the lens
▪ The lower back forms a concavity. ▪ The large concavities along the wall of the restaurant are like private rooms.
