I doubt it is the terminal, but go ahead and clean that. When it does not start are the headlights, blinkers, radio, etc working. If so then the car is getting power. Some additional detail might be needed, does it turn over, or just make a clicking noise, is there any grinding sounds? Fist thing is to get the battery tested. If possible leave battery for a full drain and charge test.
It could be a connection to the starter, if the ground wire is corroded/loose that can cause intermittent starting problems. Other possible issues, starter solenoid or ignition switch. Engine speed sensor.