Web Front End (WFE) servers are the servers in your deployment that run the Web Application service. You need to purchase one license for each WFE Server. A unique license key is provided for each WFE Server in your deployment. To determine the number of WFE servers, please log into your SharePoint Central Administration website or contact your SharePoint administrator.
The Annual License needs to be renewed on a yearly basis to continue to use the software otherwise the product will expire.