Host is not resolved but connecting via telnet, can somebody explain how?

In aws ec2 instance, rds host name is not resolved by ping or nslookup but it is still able to reach via telnet or nc how ?

~# nslookup xxxx.rds.amazonaws.com
nslookup: can't resolve '(null)': Name does not resolve

but in nc

~# nc -vv  xxxx.rds.amazonaws.com 3306
xxxx.rds.amazonaws.com (xxx.xx.xx.xxx:3306) open

Can somebody explain me How this is possible ?