Cells covered in many cilia can beat them in different coordination patterns, and the question describes one specific pattern: a wave passing down a row of cilia, one beating just after the one before it, always in the same direction.
- Undulation movement: This term usually describes a wave passing along a flagellum or a flexible membrane (as in some flagellates), not a row of separate cilia beating in sequence.
- Synchronous movement: Here every cilium in the row beats at exactly the same instant, all together, like a chorus line moving as one. That is the opposite of a staggered, one-after-another sequence.
- Metachronous movement: Each cilium beats a fraction of a second after its neighbor, so watching along the row shows a visible wave travelling steadily in one direction. This is exactly the "one after the other, in one direction" pattern described in the question.
- Effective stroke: This names only one half of a single cilium's own beat cycle (the power stroke, as opposed to its recovery stroke), it says nothing about how neighboring cilia coordinate with each other.
Only metachronous movement describes a sequential, directional wave running across a row of cilia.
Let's summarize:
- Synchronous means all cilia move together at once, metachronous means they move in a timed sequence that produces a wave.
- Undulation and effective stroke describe different things (a flexible wave or a single beat phase), not row-wide coordination.
So the sequential, one-directional wave of ciliary beating is called metachronous movement.