AB push to level off
On the Airbus pushing the ALT pb (330/340) will command the airplane to level off and maintain the new altitude (ALT HOLD engages). It will not try to return to the altitude at which the pb was selected.
Pushing the vertical speed knob (320/2330/340) accomplishes essentially the same thing, though the vertical mode becomes V/S 0 (or flight path angle 0°).
Rule of thumb: It takes about 10% of the current vertical speed to level off.