CHP means continuous horsepower. It is a new term and enhanced version of horsepower (HP). The treadmill motors with CHP are more recommended. Because CHP will give continuously the same amount of power to treadmill whether you are walking or running. But motors with HP tag will get out of order earlier as compared to CHP motors because they can't give continuously same amount of power.
When you will increase the speed of treadmill, then the HP motor has to work more quickly which will result in more pressure and thus damaging the machine. Therefore, go for that machine that has CHP motors.