Usually it’s the part of the bacon cut off to make those nice square packages and is of low quality.
But the ones I see and buy are of extraordinarily high quality- better than the average packaged bacon. It may be a local ‘thing’.
These bacon ends are in the bacon area of my local Food Lion in pink plastic 4 pound containers with a clear top.
The worst package I bought did have maybe a 1/4 lb (out of the 4 lbs) of fat-rind ‘waste’ hidden it that I used in some vegetables. So even at a quarter the price examine it closely.
Even if it's mostly fat it can be useful. Like frying it up in a skillet, whisking in a couple tablepoons of sugar and maybe 1/3 cup of vinegar and drizzling the whole mess over some greens.
It even makes dandelion greens taste like heaven.