Locus is Latin for "place", I think this means that it might have something to do with situational awareness, or control. This is all speculation, but all armor pieces (except the Bungie Armor) have an in-universe explanation, so maybe we could speculate as to what it's meant for. --Delta1138 SnooPING AS usual I see 13:57, 31 May 2012 (EDT)
Locus is a Helemt Skin, not a Helmet
http://www.bestgamesnetwork.net/2012/05/microsoft-reveals-more-halo-4-pre-order.html
The above link shows the "Locus" helmet from the front, and it says "Helmet Skin." Notice how the white forms an X. This can very well be refering to the Locus of Chromosomes; the center point. It's making me think that, as the title above states, the Locus is refering to a skin rather than a helmet. Missing Mandible 01:18, 1 June 2012 (EDT)
Code
Hello I am REACHSURVIVES. If anyone would like to trade the Locus helmet skin for the CIO Web skin, please, message my gamertag JHWRAITHSHOT.