An intermediate certificate is the certificate, or certificates, that go between your site (server) certificate and a root certificate.
The intermediate certificate, or certificates, completes the chain to a root certificate trusted by the browser.

Using an intermediate certificate means that you must complete an additional step in the installation process to enable your site certificate to be chained to the trusted root, and not show errors in the browser when someone visits your web site.

Click to visit the Complete list of Intermediate and Root Certificates

Click to find Installation instructions