Servo motors: a motor with an opinion about where it's pointing
A servo motor isn't really a distinct motor technology, it's a small system: typically a brushed or brushless DC motor, a gear train to boost torque and slow the output speed, a position sensor (usually a potentiometer or encoder), and a small onboard controller, all packaged in one housing. You send it a target angle (classically as a PWM pulse width between about 1 and 2 milliseconds), and the internal controller reads the position sensor, compares it to the target, and drives the motor until the two match, then holds that position by continuously correcting for any drift. This is why servos are so easy to use at the application level: from the outside, you just command an angle, and all the closed-loop control happens inside the housing where you never have to think about it.
That built-in closed loop is also what makes servos the default choice for robot arm joints, camera gimbals, and RC vehicle steering, anywhere you need to command a specific angle and have the system hold it against outside disturbance. The tradeoffs are limited range of motion (typically far less than a full rotation, though continuous-rotation servos exist and sacrifice position holding for speed control instead) and less raw efficiency than a bare motor, since the internal gear train and controller add friction and overhead losses. Servos are also a black box: you generally can't tune the internal control loop, so if a stock servo's response is too slow, too jittery, or not strong enough for your application, you're stuck buying a different servo rather than retuning the one you have.