I've misunderstood polyrhythm, so what is this...

There is a musical device that I love but I don't know what it's called. A simple example is as follows: Musician A plays a repeating phrase in 4/4 Musician B plays a repeating phrase in 5/4 The two phrases "slide past" each other, so that after 5 measures for musician A and 4 measures for musician B, they "line up again", both hitting the first note of their repeating phrases at the same time. To be clear, they are both playing quarters, not fifths and quarters.

I had thought this was polyrhythm, but it turns out that e.g. 5:4 polyrhythm means something very different, playing fifths over quarters (or eighths? Sorry if I mixed that up).

I checked out the FAQ, and it seems like maybe a form of polyphony, but if so I don't know what type of polyphony.

Thanks! -long time fan of music, not formally trained, listens to too much Philip Glass and jam bands