The Collaborative International Dictionary of English v.0.48:

Fungi Imperfecti \Fun"gi Im`per*fec"ti\, pl. [L. imperfecti
   imperfect.] (Bot.)
   A heterogenous phylum of fungi which lack a sexual phase, or
   of which the sexual phase is not known. Some undoubtedly
   represent the conidium stages of various Ascomycetes. It is
   not considered a natural phylum, and is also called the
   Deuteromycota. The group is divided into the orders
   Sph[ae]ropsidales, Melanconiales, and Moniliales. It
   includes the genera Penicillium and Aspergillus, which
   reproduce asexually by means of conidia.
   [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

Fungi imperfecti
    n 1: large and heterogeneous form division of fungi comprising
         forms for which no sexually reproductive stage is known
         [syn: Deuteromycota, subdivision Deuteromycota,
         Deuteromycotina, Fungi imperfecti, subdivision
         Deuteromycotina]