A brake pad that will not release keeps dragging on the rotor - you feel reduced power, a pull, and a wheel that gets very hot. It is the same family of problem as a sticking caliper, and it needs prompt attention. Here is what causes it.
A stuck caliper piston
The most direct cause is a seized caliper piston - corrosion behind a torn dust boot rusts the piston so it pushes the pad on but cannot retract; see caliper won't retract. The pad stays clamped, dragging constantly and overheating that corner.
Frozen slide pins
On a floating caliper, seized slide pins stop the caliper from floating back, so it cannot release the pad evenly - a cheaper and very common cause; see sticking caliper symptoms. Cleaning and greasing or replacing the pins usually frees it - see how to unstick a seized caliper.
A collapsed brake hose
A deteriorated brake hose can trap pressure like a one-way valve, so the caliper cannot release even though it is otherwise fine - see brake hose replacement. This mimics a stuck caliper and is easy to overlook.
Fix it before it does damage
A dragging brake overheats the pad, rotor, and fluid and wears that side fast, so do not keep driving it. Diagnose the slide pins first (cheap), then the hose, then the piston. Free or replace the culprit, then fit fresh pads and hardware.