What is a private subnet in aws?

[hawksbill]

There are subnets within AWS VPC's but how do you tell if the subnet is private or not, both public & private subnets can have private IP addresses, so that does not distinguish them.

If a subnet does not have an internet gateway - IGW, then it's a private subnet.

If a subnet does not have an IGW but is routing via a Virtual Private Gateway - VPG, then it's a VPN only subnet