Treasury Reg. 301.7701-3: Business entities; definitions  

Other business entities. For federal tax purposes --

  1. The term partnership means a business entity that is not a corporation under paragraph (b) of this section and that has at least two members.
  2. Wholly owned entities --
    (i)In general. A business entity that has a single owner and is not a corporation under paragraph (b) of this section is disregarded as an entity separate from its owner.