What are the female parts called? What is the proper term for the "female" section of the piece that the "studs" insert into? I have heard "pipes", "tubes", "underbits". Is there an actual term for the female section?
Chapter 1, Page 4, The Unofficial LEGO Builder's Guide:


  The tube is the other half of the mechanism that helps bricks stick
  together. Tubes capture the studs so that you can join LEGO elements
  and know they won't fall apart.