Blade stock thickness is the thickness of the steel at the spine, before any grinding. It is quoted in inches or millimeters on spec sheets, and it is the single best predictor of whether a knife is built to slice or to survive.
Roughly, under 0.10 inches is a slicer, around 0.12 to 0.16 is a general-purpose working knife, and 0.20 inches and up is a chopper or a hard-use fixed blade. Kitchen knives sit at the thin end, survival knives at the thick.
The number tells you about the spine, not the edge. A thick blade with a full flat grind can still cut well, because the grind decides how quickly that thickness disappears as you move toward the apex.
Every bit of extra thickness has to be pushed aside by every cut you make. Marketing tends to treat thick stock as a strength claim, but for the great majority of what people actually cut, thick stock is a tax.
Buy thickness deliberately, for batoning or prying or chopping. Do not buy it because it sounds tough.