PP&E is the long-lived physical backbone of a business: factories, vehicles, machinery, buildings. It is reported after subtracting the accumulated wear-and-tear (depreciation) charged over the years, so an aging asset base shows a shrinking figure even when nothing was sold.
Equipment-hungry businesses, manufacturing, utilities, telecoms, airlines, carry huge PP&E relative to revenue, while software, services, and brands carry little. How productively it generates sales is measured by fixed asset turnover, covered in its own entry.