What is the difference between insurance policy and insurance certificate?

There are 3 types of cargo insurance documents available in international marine cargo insurance market.

These are insurance policy, insurance certificate and declaration under an open cover.

Declaration under an open cover is not used so frequently in daily practice comparing to remaining two insurance document types. 

For this reason knowing details of insurance policy and insurance certificate is very important not only for exporters and importers but also other foreign trade participants.

Today I would like to clarify the differences between an insurance policy and insurance certificate on this article.