This article is from the FAQ, by with numerous contributions by others.
An H-1B classification is temporary (three years, extendable for
another three). People loosely refer to H-1B as H-1. So they are
the same thing. The following variations exist within H-1:
H-1A Registered Nurse
H-1B1 Specialty Occupation (Professionals)
H-1B2 U.S. Department of Defense special visas
H-1B3 Artists, entertainers or fashion models of national or
H-1B4 Artists or Entertainers in unique or traditional art form
H-1BS Essential support personnel for H-1B entertainer or athlete.