Function as a Service (FaaS) is an event-driven subset of serverless computing that allows developers to write and deploy code without worrying about servers or infrastructure management. FaaS solutions are different from Platform as a Service (PaaS) solutions because functions are completely event-driven and stateless. Developers can use FaaS to save significant resources and reduce costs by combining long-running servers with on-demand reactive functions. To use FaaS appropriately, make sure that each event triggers only one function, keep functions short-lived, maintain statelessness, test and configure functions locally, and ensure security by keeping secrets out of source code and granting permissions only for necessary tasks.