Γ is a group of central type if it
possesses an irreducible complex character of degree |Γ :Z(Γ)|1∕2. This is the largest
possible degree for an ordinary irreducible character of a finite group. A group G
which is isomorphic to Γ∕Z(Γ), where Γ is some group of central type, is called a
central type factor group (ctfg). A variety of restrictions on ctfgs are found. These
include a local characterization of ctfgs, and restrictions on normal and subnormal
structures of ctfgs.