All the Lambda-based applications which are also termed as serverless application. These functions are composed of functions that are triggered by events. A normal serverless application can consists of one or more than one functions which can be triggered by events e.g. object uploads to Amazon S3 or API actions. These functions can stand alone or leverage other resources such as DynamoDB tables or Amazon S3 buckets.
The most basic serverless application is simply a function that you create in Lambda.
AWS Lambda is basically a serverless platform where you just upload and execute your code.