Topical authority describes how completely a site covers one subject rather than how strong any single page is. A site with sixty connected pages on commercial refrigeration answers questions a site with three pages cannot, and it tends to rank for queries it never targeted directly.
Building it is mostly inventory work. Map the questions a buyer asks from first awareness through comparison to post-purchase, and check which ones have a page and which do not. The gaps are usually unglamorous: specifications, compatibility, maintenance, cost of ownership. Those are the pages that convert and the ones competitors skip.
Internal linking is what turns a pile of pages into a subject. Pages that reference each other along real relationships give crawlers a structure to follow and give readers somewhere to go next. Orphaned pages contribute almost nothing regardless of quality.
Two failure modes are common. Publishing thin pages to fill a keyword grid creates competing near-duplicates instead of depth. Covering too many unrelated subjects splits the same effort across topics and leaves none of them complete.