Well, that depends. You certainly want to ensure the availability of the information under your remit isn't compromised by a threat actor, but reducing your attack surface by, say, shutting down external internet access is certainly a valid mitigation in some circumstances.
I didn't know either, so I looked it up: The three initials stand for the three most important IT protection goals, often referred to as the "pillars of data security":
Confidentiality,
Integrity,
Availability.
There are other IT protection goals, including authenticity, privacy, reliability, and (non)repudiation.