Function-as-a-Service (FaaS) is an event-driven computing execution model where developers write logic that is deployed in containers fully managed by a platform, then executed on demand.

In contrast to BaaS, FaaS affords a greater degree of control to the developers, who create custom apps rather than relying on a library of prewritten services.

Code is deployed into containers that are managed by a cloud provider. Specifically, these containers are:

Stateless, making data integration simpler.

Ephemeral, allowing them to be run for a very short time.

Event-triggered, so they can run automatically when needed.

Fully managed by a cloud provider, so that you only pay for what is needed, not always-on apps and servers.

Using FaaS, developers can call serverless apps through APIs which the FaaS provider handles through an API gateway.

https://www.ibm.com/th-en/topics/faas