Basic explanation of baryon acoustic oscillations; what if anything is actually oscillating? Sci-News' Sloan Digital Sky Survey Collaboration Releases New 3D Map of Universe links to the two videos

The eBOSS 3D map of the Universe
SDSS releases largest 3D map of the universe ever created

and says

The team’s results will be published in a series of 20 papers in the Monthly Notices of the Royal Astronomical Society.

After 01:30 in the second video Jiamin Hou from the Max Planck Institute for Extraterrestrial Physics says:

However the red shift has an additional component that is due to the galaxy’s own velocity, and which moves in response to the gravitational attraction of the surrounding matter, and these two components can not be separated from each other. But the statistical analysis of the eBOSS allows us to distinguish the effects of velocity from that of expansion.

I've also looked at:

Wikipedia: Baryon_acoustic_oscillations; Cosmic sound
SDSS.org's surveys; eBOSS

but I can't get a grasp of what the term &quot;baryon acoustic oscillations&quot; really means.
Question: Is it possible to write or quote a basic explanation of what these are? For example, does oscillation mean there are things moving back and forth due to some restoring force? Is there something analogous to a &quot;sound wave&quot; out there somewhere? Or is there just a plot of something that shows a wiggly line that goes up and down?
tl;dr nothing is oscillating now, but it was in the early universe. Now we just see the frozen relics
This is just an attempt at a simplified explanation of the Wikipedia article linked in the question.
There were pressure waves in the very early universe. They came from a balance of gravity and radiation pressure (the matter at the time was hot enough to be opaque). Whereever there happened to be a locally higher density (of matter, radiation and dark matter) the excess pressure would cause an expansion and then gravity would cause a contraction sending waves out at (according to the article) half the speed of light.
As the universe expanded and cooled, matter eventually became transparent (it was hydrogen and helium gas) letting the radiation pressure escape and leaving higher densities both in the location of the original concentration and at the crest of the wave a certain distance away (but the same certain distance for the first waves from each concentration). Those high densities are where the galaxies formed, so what we look for today is an excess of galaxies at a specific separation and that's what we see.