A CNAME or Canonicial Name record is a type of DNS record. It is used to create aliases. A CNAME record points a domain/subdomain to another domain/subdomain.
For example, your main domain is companyname.com; you also have the domain companyname.com.ng which you want to point to your main domain. You would achieve this by setting up a CNAME record. Thus, anytime a website visitor types in companyname.com.ng, they will see the same content displayed on compnayname.com.
NB: A CNAME record always points to another domain/subdomain and not an IP address.