The trust relationship between the primary domain and the trusted domain failed. what does this phrase mean?

It's an error message

Explanation:

This error indicates that this computer in no longer trusted and diconnected from the Active Directory since the local computer password doesn’t match this computer object password stored in the AD database. Trust relationship may fail if the computer tries to authenticate on a domain with an invalid password. Typically, this occurs after reinstalling Windows.

A system trusted by a user, is one that the user feels safe to use, and trusts to do tasks without secretly executing harmful or unauthorised programs; while trusted computing refers to whether programs can trust the platform to be unmodified from that expected, whether or not those programs are innocent, malicious or otherwise.