An axiomatic definition of a
pseudoconvex class of functions is developed. The models include classes of
subharmonic, plurisubharmonic, q-plurisubharmonic, convex and q-convex functions,
and many others. Notions of dual class of functions and of pseudoconcave and
pseudoconvex sets are introduced and studied. The results have applications to
complex interpolation of normed spaces, given elsewhere.