NAT Gateway is a service provided by AWS that allows customers to establish secure communications between their virtual private clouds (VPCs). It enables users to securely connect applications and systems running in the AWS cloud with resources located in their own networks. NAT Gateway provides a secure and resilient connection between VPCs and other networks, including private data centers, public internet, or corporate networks. It eliminates the need for customers to set up multiple NAT devices and configure complex IP routing rules. NAT Gateway also simplifies network security compliance by allowing customers to limit access from specific sources within their VPCs.