means A broad, flat, thick piece of something solid — stone, concrete, wood, or even cheese — usually with a level top and considerable heft.

from From Middle English 'slab,' meaning a flat slat or thick slice, of uncertain origin — possibly related to similar words in Scandinavian or Old French, but the trail goes cold early. For centuries it named the rough outer plank cut off a log, then spread to any thick flat cut, eventually settling comfortably onto the poured concrete it describes today.