The concept of material information sits at the heart of how insurance works. Insurance is a contract of the utmost good faith, which is a formal way of saying that both sides, the insurer and the policyholder, have to deal with each other honestly. On the policyholder's side that means disclosing anything that's material to the risk being insured.
In pet insurance terms, material information is essentially anything that a reasonable insurer would want to know when deciding whether to cover your pet and at what price. Your pet's breed, age, health history, any conditions they've been treated for, any symptoms they've shown — these are all examples of information that's likely to be material.
The tricky part is that the test for materiality isn't whether you think something is important. It's whether a reasonable insurer would think so. A bout of diarrhea that resolved in two days might feel trivial to you but if the vet noted it, it's on your pet's records, and an insurer may consider it material information about your pet's health history.
This is why the advice on pet insurance applications is generally to err on the side of disclosing rather than deciding something isn't worth mentioning. The consequences of failing to disclose something material are potentially serious, and the decision about whether it affects your cover is the insurer's to make, not yours.
"The test for materiality isn't whether you think something is important. It's whether a reasonable insurer would think so."