Decurion

Could someone explain to me what this "Decurion-style" detachment is?

I first heard it with the Necrons, and now I am hearing people refer to the new C:SM as having a decurion... And now here I am, just a guy, not knowing WTF any of that shit means... haha

A "Decurion-style" detachment can be described as, in short, and Ur-Formation.  It's generally called a "Decurion-style" because Codex: Necrons were the first to do this style of list building, and thus all subsequent instances were/are compared to them.

What Ur-Formations like these do is they are a formation build almost purely out of other formations.  The component formations will be described as modules you can plug and play into the larger framework, giving you increased power out of what you use in your list, in exchange for being far more restricted in how you build said list.  Many of the component formations will contain units that are considered meh-thru-bad in an attempt by GW to move stock that isn't selling, but giving you boost to them and the units you take with them in exchange.

So the new SM decurion is what - the Demi-company?
What others have decurion styles

It started with the Necrons, and is now in the Eldar, SM, and DA, and Daemonkin books. I would expect this formation to stay around for a while. It's basically an army-sized formation that provides various extra bonuses to the whole thing. Example, the Necron Decurion allows the army to pass get up rolls on a 4+ instead of a 5+ and some other nice benefits. There is a catch to running these things however, in that it reduces your flexibility in what you can then add to the army, as you are no longer using the CAD. You can only add extra stuff in the form of the other formations.

Spamus Eatus wrote:It started with the Necrons, and is now in the Eldar, SM, and DA, and Daemonkin books.  I would expect this formation to stay around for a while.  It's basically an army-sized formation that provides various extra bonuses to the whole thing.  Example, the Necron Decurion allows the army to pass get up rolls on a 4+ instead of a 5+ and some other nice benefits.  There is a catch to running these things however, in that it reduces your flexibility in what you can then add to the army, as you are no longer using the CAD.  You can only add extra stuff in the form of the other formations.  

But these formations in the non-necron books are not called Decurion though, right?
It's confusing to me since I don't really delve and read the other codices, and when I read things online and they refer to non-necron decurion I have NO clue what they are talking about.

No, they're called other things, the SM big one is the Demi-Company. 2 can be fielded as a Battle Company. They're just all referred to as Decurion detachments since Necrons did it first

actually, the space marine one is called a Gladius Strike Force. that's their "decurion". a Demi-Battle Company is the required minimum formation choice to field it. a Demi-Battle Company is what you saw me field against you the other week, matt. it's one of the nicer formations out there, because it gives every model that's from the Demi-Battle Company the Objective Secured rule