Almost all fiduciary professional liability policies are “claims made” policies. There are other types of policies called “occurrence policies,” more typically in the general liability context – i.e. bodily injury and property damage, but these are very rare in the fiduciary professional liability world, so we will not discuss them further here (please contact a presenter to discuss them further).
In the claims made context, the insurance policy will typically say (in the first paragraph or so) that it provides coverage for a “Claim” (a defined term) first made during the policy period - and, in most instances, reported during the policy period too. So it is the making of a “Claim” that “triggers” the coverage available under the policy.
Many policies define Claim as “a demand received for money or services.” Some people do not realize that a Claim therefore does not have to be a lawsuit. A letter or email from a client accusing you of making a mistake and seeking to hold you responsible can be deemed a Claim. Even a verbal demand can qualify.