Stuck or Sticking Brake Caliper
Calipers do seize up, the pistons mostly. If there are a lot of miles on the vehicle (60,000 miles) and a caliper seizes, the one on the other side will follow shortly. Consider replacing them both. Two other possibilities are: guide pins not sliding for some reason, flexible brake hose collapsed internally. Most likely it's the piston issue.
When replacing the caliper make sure you know the torque specifications for: pins, caliber bracket, banjo nut, lug nuts. Use non oil based synthetic brake lubricant. Don't let the caliber hang from the hose while you are working. Watch out for some replacement calibers, they may, or may not, have pins with them. Avoid brake calipers that have phenolic pistons.
The sticking caliber comes and goes, usually coming at the worse times, like in traffic. Pushing the petal hard will do it, generates a little heat and a stuck piston. Next time it sticks, if at home, jack the vehicle up, block it up temporarily, back off the banjo bolt (hose to caliber) some (see fluid coming out) from underneath and see if the brake frees up. If this pressure relief frees up the brake then the hose is the problem. You could run the vehicle up a ramp and do this as well. Considerations: - Caliber isn't new any more, it has been heated up badly by whatever means, and is going to let you down prematurely anyway. Replace it. Consider the other side as well, it's next sooner than you think. - The rotor can be turned down and cleaned up (beat out the rust, paint with "rust fix" along the circumference) and will look no different than a new rotor in a year's time. I would stick with the original equipment rotors for as long as I could. There's lots of "new" junk" rotors out there, some of them not fitting that great with regard to the pads binding. Some pads are bad too. - Do you have the Teves brake system (have to remove the caliber bracket to replace the rotor)? If so, you have to be very careful to get the right parts. Hope all this helps. Been there, done that many times.