In one sentence
Topical Authority is the authority a site earns by covering a specific theme deeply and comprehensively across the whole site. It is an evaluation axis by which Google and AIs decide that "this site is an expert on X."
What does it look like in practice?
For example, building Topical Authority around the theme "GEO" might look like:
geo-meters.com/learning/
├── Handbooks (three complete guides)
│ ├── GEO Basics complete guide
│ ├── GEO Implementation complete guide
│ └── GEO Management complete guide
├── Glossary (40+ terms)
│ ├── GEO / AEO / LLMO
│ ├── Schema.org / llms.txt / FAQ Schema
│ └── ChatGPT / Claude / Gemini / ...
└── Latest articles (monthly reports + industry trends)