Good for you, Squeak, the best way to learn is to ask.
Go to this link; look at Part #2 in the diagram, and then look at the first photo below the diagram. It's commonly referred to as a Barrel Bushing.
Some, like my 1980 Series 70 Govt Model, had a barrel bushing with spring-type flanges, meaning that instead of a solid "tube", the bushing has slits in it that give it a spring-like grip on the barrel. They can sometimes be a bugger to remove. Never heard of them breaking, but I haven't heard of everything. But, as ka64 noted, they're tighter, so they stabilize the barrel a bit more.
I bought the replacement, solid bushing and haven't noticed too much play in the barrel affecting accuracy. Note that Colt doesn't offer the other bushing any more.