We still have no idea or not much what could the Guardians mean. I said/wrote many times just like some of us that Guardians is a reference for the Forerunners, because the Didact said: “We are Forerunners, guardians of all that exists”
But a few minutes ago I watched (again) the Halo 3 Vidoc. In that video (at about 3:43 - nice timin’)Joseph Staten said that Cortana is Chief’s “guardian angel”. So from that, what if the Guardians means those persons who wan’t to protetct Chief?
What do you think?
Yeah, that could be possible. Whenever I think of Guardians all that comes to mind is those D-bag beam towers on Sandbox in Halo 3. 
I think “Guardians” refers to both the original Guardians (Forerunners) and new (humans; Chief specifically). After all, humans taking over the mantle was the Librarian’s plan all along.
There are a lot of theories out there, but i like where you guys are going, i am so excited for this campaign
Halo 5 Guardians: The Master Chief and Agent Locke go on a quest to learn about the random forces that kill you when you leave the boundaries of the map.
> 2533274802469862;4:
> There are a lot of theories out there, but i like where you guys are going, i am so excited for this campaign
Ha ha I know right. Time is dragging!