Many believe this term to mean the Universe in which the Halo video game series takes place, however it was officially defined some time ago by Bungie themselves.(the Video Game company that created the Halo series among others)
1.) www.RedvsBlue.com and www.Halo.Bungie.org are some of the larger sites of the Haloverse.
2.)I'm very disapointed to only just now see this posted here. Someone in the Haloverse dropped the ball on this one. lol