Java API for RESTful Web Services (JAX-RS) is a framework for building web services based on the REST (Representational State Transfer) architectural style. It provides a set of Java APIs for building RESTful web services, which can be used to create lightweight, scalable and maintainable web services. JAX-RS is a software skill that involves using Java programming language and related tools to create web services that can be consumed by other applications over the network.