Plain version: concealment is staying silent about something you know and should have said. You told no lie; the problem is what you left out.

California Insurance Code §330 defines concealment as neglect to communicate that which a party knows and ought to communicate. Under §332, what a party ought to communicate includes material facts within its knowledge that the other party has no means of ascertaining.

Example: a restaurant owner knows her kitchen fire suppression system failed its last inspection. The insurer has no way of learning this, and she says nothing. Everything she did say is accurate, so this is not misrepresentation, which requires a false statement. It is concealment.

The effect (§331): concealment, whether intentional or unintentional, entitles the injured party to rescind the insurance. An honest mistake does not remove that right. Whether the fact mattered is judged by materiality (§334), not by whether it caused a later claim.