An alias is a DNS record with a name that resolves directly to an ip_address.
A cname has also an alias functionality but as it resolves a name to another name and not to an ip address, the DNS resolver needs therefore another roundtrip to get the final ip_address. The CNAME record is then slower than an ALIAS record.
Before creating an ALIAS record, check there are no:
set for the same Host (e.g., yourdomain.tld or example.yourdomain.tld) because they can conflict with each other.
As ALIAS is not an RFC compliant DNS record, it may be not supported. In this case, you need to use a CNAME instead.