The choke collar is also called a choke chain, slip chain, or check chain.
A choke collar consists of a length of chain or nylon rope with rings at
either end such that the collar can be formed into a loop around the top
of the dog’s neck, just behind the ears. The ring which connects to the
leash goes over the back of the dog’s neck, not under. When the leash is
attached to the dead ring the choke collar does not constrict on the dog’s
neck. When the leash is attached to the live ring the chain slips tighter
when pulled and slips looser when tension is released. Dog training occurs
via a quick gentle jerk with an immediate release. This is called a check
(hence the name check chain), leash pop, snap, or correction, and is used
to alert the dog that it has done something undesirable.
The reference to choking is due to the fact that the choke chain typically
has no limit to how far it can constrict on the dog’s neck. The name "choke
chain" is deceiving however, as proper use of this training device
does not involve choking the dog. Even so, it is important to note that
improper use of a choke chain can result in injury and even death of the
dog, for the aforementioned reason. Dogs should never be left alone with
a choke chain on in case the live ring catches on something.