AWS : IGW vs NATGW

https://medium.com/awesome-cloud/aws-vpc-difference-between-internet-gateway-and-nat-gateway-c9177e710af6

Internet Gateway (IGW) allows instances with public IPs to access the internet.
NAT Gateway (NGW) allows instances with no public IPs to access the internet.

IGW allows Outside traffic to go in

NAT-GW does not allow Outside traffic to come in, It only allows from inside to Outside