The short definition
AI visibility is how likely a large language model is to mention your business, accurately, when someone asks it a question you should be the answer to.
It is not a ranking position. There is no page two. Either you are named in the answer or you are not part of the conversation.
Why it's different from search
A search engine returns a list and lets the buyer choose. An assistant makes the shortlist for them, usually naming two or three options with a sentence of justification each.
That compresses the market. Where ten businesses used to get a look, three now do — and the ones that get named tend to keep getting named, because the sources that describe them keep being cited.
What models are actually looking for
Clarity about who you are: consistent naming, services, locations and structured data that agree with each other everywhere they appear.
Corroboration: credible third parties describing you in the same terms you describe yourself.
Quotable substance: pages that answer a question directly, with specifics a model can lift without hedging.
Where to start
Ask the assistants the questions your customers ask. Write down who gets named and what sources are cited. That baseline is uncomfortable and extremely useful.
Then fix the unglamorous things first — structured data, consistent profiles, clear service pages. Most businesses are invisible for technical reasons long before they're invisible for authority reasons.