The underwriting period is a limited time period at the beginning of a new policy when the insurer may gather the necessary information about an applicant and make a final decision on that applicant's acceptability.
During this time period (typically 30 to 90 days, depending on the line of business and the state where the risk is located), the insurer is free to cancel the policy for any legal reason. Once this time period has passed, then the insurer is limited in the reasons for which it may cancel the policy.