The line regulation is the change in the output vs. the change in the input voltage.
The load regulation is the change in the output vs. the steady-state load current.
The stability is a complex subject. There is output ripple, which you might find specified on the datasheet.
There is also transient response, which is the deviation from the nominal output voltage due to a change in load current.
This includes overshoot and undershoot. It's not typically specified for a general purpose supply because the load excursion and dI/dt depends on the specific application. Here's a sample transient response showing the output voltage, load current and the inductor current. Note the undershoot on the rising edge and overshoot on the falling edge of the load:
The transient response does correspond in a general way to the phase margin of the control loop (though there are many caveats) so if the phase margin is specified it can be a general guide to the transient response.
The entire deviation from the ideal value output under all conditions comes from line regulation, load regulation, initial regulator accuracy, ripple and transient response together.