The difference between crystal resonators and crystal oscillators

The quartz wafer, plated with electrodes, is mounted on a stand, and the shell is added to make a quartz crystal resonator (which is what we see with two legs).

The quartz crystal resonator, coupled with oscillating, amplifying or shaping circuits, is packaged into a metal shell to become a quartz crystal oscillator, which generally has four terminals (power end, ground, output, and a voltage control or suspension terminal).

Quartz crystal resonator is a passive device.

Quartz crystal oscillator is called crystal oscillator. The quartz crystal must be connected to the oscillation line to have a signal output, and the crystal oscillator itself has an oscillation circuit, so there is a power supply to have a signal output. It's an active device.