Its name is a duplicate of the previous record, so in your example, it would be a 'www' Address record. In your example, the second '@ A' record does not need the '@'.
Your example with a CNAME is invalid, as a CNAME cannot have another record with the same name. As I recall, older versions of BIND only warned about this, but newer ones won't load a zone with these errors. Other types of records are valid - that's how you add multiple addresses for names (client-based DNS round-robin), or multiple (primary, secondary, and tertiary) MX or NS records for domains, for example.
$TTL 120
$ORIGIN mywebsite.com.
@ NS mynameserver.com.
@ A 112.134.156.178
www CNAME mywebsite.com. ; Invalid, CNAME cannot share with an A record
www A 111.122.133.144
file CNAME mywebsite.com. ; Alias of www.mywebsite.com.
What you should see in zones is similar to this:
$TTL 86400
$ORIGIN example.com.
; nameservers in another domain - must point at A records
@ NS ns1.example.net.
NS ns2.example.net.
; mail hosted elsewhere - must be A records
MX 10 mail.example.net.
MX 20 backupmail.example.net.
; web farm - nameserver will return both A
; records when requested and client will alternate between them
www A 192.0.2.200
A 192.0.2.201
; points at www.example.com. - in this case both CNAME (www.example.com.
; and A records (192.0.2.200, 192.0.2.201) should be in the response returned.
www2 CNAME www
