An Entity ID is something that you choose as a SP. This page should help you choose a good entityId for your shibboleth configuration.
Picking an entity ID
First, you should review the official Shib Wiki page on entity naming.
Before you can configure your application to work with Shibboleth, you'll need to choose an Entity ID. This id uniquely identifies your web application or set of web applications across all shibboleth federated IdPs and SPs. One entity can service multiple servers and web applications. The easiest way to choose this is to use a URL. For example:
This allows you to setup this URL as an actual web page that can provide access to your department's entity metadata. You can create multiple entities if you need to to distinguish between different classes of web applications. Example Entity IDs could be: