oblique motion
One voice holds while the other moves.
One voice holds a note while the other moves. Because only one line changes, oblique motion is inherently safe and independent, and it is the easiest way to keep voices from colliding. A pedal tone under a moving melody is oblique motion writ large.
Learn it: Motion types
The one-sentence definition at the top is the same one the Theory Aide extension shows as a tooltip inside Ableton Live. Hover any dotted term for its own.