Actionable price
An actionable price is one currently available at a venue you can actually bet, on the terms stated.
In plain English
Actionable is stricter than visible. A number in a screenshot, at a book you cannot access, or in a market too thin to take your stake is not actionable.
Example
A quote exists at an offshore book you have no account with. It is a real price and not an actionable one for you.
Why it matters
Records built on prices nobody could take are not records of anything achievable.