EC2 local-ip vs public-ip

In EC2 there are 2 ips and 2 hosts ---
running ec2metadata
displays instance descriptions and 4 items (Actually 2, is very important to setup inter cluster

1) local-ipv4: <<>>
2) public-ipv4: <<>>

Other 2 are 3) local-hostname: <<>> 4) public-hostname: <<>>

local-ipv4 is the one used to other Ec2 instance.