What is "lufbery circle"

The Lufbery Circle, or Lufbery Wheel, also spelled "Lufberry" or "Luffberry", is a defensive air combat tactic first used during World War I.

While its name derives from the name of Raoul Lufbery, the leading fighter ace of the Lafayette Escadrille, he did not invent the tactic; how it acquired this name is not known, although it may be from his popularization of it among the incoming U.S. pilots he trained. In non-American sources it is in fact usually referred to simply as a "defensive circle".