Double concave lens has two inward curved surfaces. Double Concave lens has negative focal length.

Biconvex Lenses- Applications
These lenses have around a number of uses of which some of them are listed below-

Biconvex lens are used as magnifying or condensing lenses.
They are also used as objectives or magnifiers
These are utilized in many imaging systems such as the telescopes, monocular, microscopes, binoculars, cameras, projectors, etc.
These are used in producing the virtual image in case of a human eye and a real image in case of the photographic films or an optical sensor
These lenses are also used as a burning-glass.
These are used in the applications of image relays and also in various kinds of industries