A two "stage" trigger has a long, light take up then until the second heavier hits. So you can "take up the slack" and then hold until you add additional pressure to press through the second stage. My "Precision" Rifle has this type of trigger.
My ARs have single stage triggers (i.e. no take up)
I have a really nice two stage trigger on my M1A. I love it. My question is why have two stage triggers? Is it to give an added level of safety when shooting? For example, when shooting the 200 yard standing I know that I have to take up that first level of slack before I shoot. That way there is little chance of me touching off a shot on accident while getting into position or something to that effect. Just curious.
Good question though Steel, around here it is better to ask those seemingly easy questions and be informed rather than going around acting like you know what you are talking about and really making an ass out of yourself.
The longer first stage of the trigger pull acts as an additional safety device, making it safe for the second stage, which has more of an effect on bullet travel, to be lighter than would otherwise be safe.
On the better 2 stage triggers you can set them up so the take-up stage carries most of the weight, with maybe a 1 lb or less on the second stage. That's how I set the Jewell up on my AR Service rifle.