PostEaseThe short answer
Topical authority is the degree to which an account or a website is recognized, by readers and by search engines, as a trustworthy source on a specific subject. It is built through consistent, substantive coverage of that subject over time rather than a single piece of content.
Depth and consistency matter more than a single strong piece
One excellent piece of content on a topic demonstrates competence once; a large body of consistently substantive content on the same subject area demonstrates genuine, ongoing authority. Search engines and readers both tend to trust the latter more, since it is harder to fake than a single good post.
Why this matters for a content strategy
A content plan that jumps between unrelated subjects builds less topical authority in any one of them than a plan that consistently returns to a focused set of subjects. That is the same reasoning behind picking a small number of content pillars rather than covering everything loosely.