Bilateral Extended Reporting Period Provision
  
Companies get insurance policies in case a claim is made against them. These are (unoriginally enough) called claims-made policies.
If a claims-made policy is cancelled or terminated or allowed to expire, this can lead a gap in coverage. A claim filed after the policy had terminated wouldn't be covered; the company would be on the hook for the costs, rather than the former insurance provider.
An extended reporting period eases this problem. This provision extends the period for a claim to be filed, allowing situations that arise after the policy has terminated to be covered (up to a certain point).
So much for the "extended reporting period provision." The "bilateral" part comes in if the extended reporting period can get activated, no matter who canceled the insurance...the company buying the insurance or the provider. Otherwise, the clause is known as the "unilateral extended reporting period provision."