AWS Certified Solutions Architect Associate Test 2

You can use a NAT device to enable instances in a private subnet to connect to the Internet (for example, for software updates) or other AWS services, but prevent the Internet from initiating connections with the instances. AWS offers two kinds of NAT devices? A NAT gateway or a NAT instance. We recommend NAT gateways, as they provide better availability and bandwidth over NAT instances. The NAT Gateway service is also a managed service that does not require your administration efforts. A NAT instance is launched from a NAT AMI. You can choose to use a NAT instance for special purposes.
Reference: http://docs.aws.amazon.com/AmazonVPC/latest/UserGuide/vpc-nat.html