AWS Greengrass is a service from Amazon Web Services that extends cloud capabilities to local devices. It allows devices to act locally on the data they generate while still using the cloud for management, analytics, and storage. This enables faster response times and reduced latency for applications that require real-time processing. With AWS Greengrass, developers can run AWS Lambda functions, manage device communication, and securely transmit data between devices and the cloud. This service is particularly useful for Internet of Things (IoT) applications, where devices need to operate efficiently even when disconnected from the internet.