Step Function is a serverless service provided by AWS that’s aimed at making it easier and quicker to link AWS-based serverless functions and other AWS services into “steps”, where the output of one function becomes the input of the next function.
While it’s certainly possible to accomplish this without the use of step functions, AWS Step Functions offers a visual workflow editor, and it automates elements such as retry handling and tracking that would otherwise need to be coded manually. In other words, serverless step functions take some of the development work out of the hands of developers, and handle it automatically in the cloud.
“Step Functions” is a product offering that is specific to AWS, but the other major cloud vendors do have similar offerings such as Azure Logic Apps and GCP Workflows.