AWS Lambda is a serverless compute service that runs code in response to events. It allows uploading code that can be run without having to manage infrastructure. Lambda manages capacity, scaling, monitoring, logging and security patching. Events from over 15 AWS services can trigger Lambda functions. Examples include S3 bucket uploads, DynamoDB changes, and API Gateway requests. Lambda functions support Node.js, Java, Python and C# and can be used to build automated workflows like resizing images or integrating apps. It offers 300 seconds of compute time per function for free each month.