WhatA DNS record that makes one domain name an alias of another (the canonical name).
WhyResolvers follow the alias to the target domain instead of using an IP address directly.
TargetA property of a DNS record, not a number — a name either is an alias or it isn't.
The one thing to remember
A CNAME points a name at another name, not at an IP address. Resolvers follow the alias to the target domain.
In one line
A CNAME (canonical name) record in DNS makes one domain name an alias that points to another domain name — the canonical, true name. DNS resolvers follow the alias to the target domain instead of using an IP address directly.
Sources
Not medical advice. Plain-language summaries of authoritative sources; "optimal" targets are one reading of the literature, tighter than lab-normal. Every treatment decision is a clinician's.
glossary.gf.cx · dns · cname