The certificate holder is whoever is named in the lower-left box of an ACORD 25, typically the general contractor requesting proof of insurance. Being listed there means you receive the certificate and, on most forms, a notice if the policy is cancelled.
A common and costly misconception is that certificate holder status equals coverage. It does not. To actually be protected under a sub's policy, the GC must be named as an additional insured by endorsement, not merely listed as the certificate holder.