Topical authority is earned by covering a subject comprehensively and coherently — the core concepts, the adjacent questions, and the practical details — rather than publishing scattered one-off posts. Engines infer that a site which thoroughly covers ABA marketing, for example, is a better source for ABA-marketing answers than a generalist that mentions it once.
It is built through topic clusters (a pillar page plus supporting content that interlink), consistent entities, and genuine expertise. In the AI era it doubles as a retrieval signal: the more authoritatively you cover a topic, the more likely a model grounds its answer on you.