What is "Quality" in the Export Settings for JPEG?

[FloCSSDM]

Hi! Trying to figure out what element(s) of the image the "Quality" setting for JPEG changes, it's in the "Export Settings", explained here: https://affinity.help/photo2/en-US.lproj/index.html?page=pages/SizeTransform/imageSize.html&title=Changing image size.

Since I am essentially batch-resizing JPEGs by changing the "Quality" percentage, in this specific case from 100% to 30%, and making no other changes to the image, I still export them as JPEGs, what is it that I am exactly that I am reducing? Is it simply scaling down, as in decreasing the number of pixels? Sorry if this is a bit basic!

[NotMyFault]

See https://en.wikipedia.org/wiki/JPEG and the section Effects of JPEG compression

Jpeg uses a combination of multiple compression techniques to achieve high compression ratios of 1:10 or 1:100. it keeps the original overall resolution, but reduces the details within smaller 8x8 blocks.

[R C-R]

2 hours ago, FloCSSDM said:

what is it that I am exactly that I am reducing? I

Should you prefer not to read the Wikipedia entry* the TL;DR answer is pixel level detail.

* But it is a good idea to do so.