The Intermediate Certificate acts as a middle-man between TrustCor and the end-user SSL.
A Root CA is a Certificate Authority (in this case, TrustCor) that owns one or more trusted roots.
That means that they have roots in the trust stores of the major browsers.
Intermediate CA is a Certificate Authority (TrustCor) that issues off an intermediate root.
They do not have roots in the browser’s trust lists, instead their intermediate roots chain back to a trusted third-party root (the root from TrustCor).
You can download the Intermediate Certificate and Root Certificate directly from TrustCor here:
You can find more information about installing TrustCor SSLs from their Knowledge Base here.