Concavities

from The Collaborative International Dictionary of English v.0.48

Concavity \Con*cav"i*ty\, n.; pl. {Concavities}. [L. concavitas:
   cf. F. concavit['e]. See {Concave}.]
   A concave surface, or the space bounded by it; the state of
   being concave.
   [1913 Webster]