ACORD 25, formally the Certificate of Liability Insurance, is the form nearly every COI you receive is built on. ACORD is the nonprofit that standardizes insurance forms, so the layout, with its general liability, automobile, umbrella, and workers' compensation boxes, is consistent across carriers.
Knowing where each limit and date lives on the ACORD 25 lets a GC scan a certificate quickly and spot gaps, like a missing additional insured line or a policy that expires mid-project. The form itself carries a disclaimer that it confers no coverage, which is exactly why endorsements still matter.