AWS Lambda is a serverless compute service that AWS provides that allows you to run code without provisioning or managing servers.
Amazon SNS uses a publish/subscribe (pub/sub) messaging model, and does not require you to set up the notification server. Instead, you create topics, to which you push messages. Interested subscribers read messages from these topics.
Policies are JSON documents that define permissions. They specify who can access resources and the actions that they can perform. Policies can be attached to users, groups, or roles.