What is the difference between choke hold and headlock?

A choke hold is used to take control of someone by causing a restriction to their air way thus taking away their ability to fight back.

A headlock is used to just control the head without causing constriction to the air way of someone. Such as wrestling.

There are two main classifications: Air Hold and Blood Hold. The air hold is where pressure is applied to the front of the neck to restrict breathing. The blood hold is a somewhat similar position, but here the pressure is applied to the carotid artery on each side of the neck. This temporally restricts blood flow to the brain. The basic result of both holds is to cause the individual being restrained to momentarily blackout. The air chocke hold will often cause damage to the windpipe or the hyoid bone. Law enforcement is trained to use the blood hold when trying to get control of a combative person.

A choke hold is simple. When someones forearm is firmly putting pressure on the front side of neck and restricting the air passages. Head lock is when the other side of the elbow is bent at the chin area and most of the pressure is on the left and right side of the head. Headlock is basically above the neck area.

They are different names for the same manuever/hold. Front Chancery, Sleeper hold, Facelock are other names.