Incidental damage is a context-dependent description of damage associated with another event or activity. An estimate should explain the actual condition rather than rely on this label.
What this means at your property
Removing a cabinet to reach a leaking pipe may expose trim or finishes that also need attention. The access work and any resulting repair should be described separately from the original water damage so responsibilities are clear.
Does the term establish who pays?
No. Ask the project contact to identify the item, cause as understood, proposed repair and approval required. Contract and insurance questions need their own review; a glossary label does not resolve them.