means Selling goods in large quantities, usually to retailers rather than the public, at lower per-unit prices — or, more loosely, doing something on a sweeping, indiscriminate scale.

from A plain compound of "whole" and "sale," surfacing in late Middle English as "whole sale" — meaning a sale of goods in their whole, undivided lot, rather than split up and parceled out piecemeal ("retail," from a French word for cutting into pieces). The merchant who bought the whole batch paid less; the sense of "in bulk" naturally stretched into "in sweeping quantity," giving us phrases like "wholesale slaughter."