A private, high-bandwidth physical connection between an on-premises network and Google Cloud that avoids the public internet. Dedicated Interconnect connects directly at a colocation facility; Partner Interconnect does so through a supported provider.
The typical ACE question is which to pick: if the company is not in a Google colocation facility, Partner Interconnect. For encrypted connections over the internet, Cloud VPN.
Cloud Interconnect is a concept that can show up on the exam. Check the full guide to see it in context.