The Spring framework (shortly, Spring) is an application framework that is part of the Java ecosystem. An application framework is a set of common software functionalities that provides a foundation structure for developing an application. An application framework eases the effort of writing an application by taking out the effort of writing all the program code from scratch.
We use Spring in the development of many kinds of applications nowadays, from large backend solutions to automation testing apps. According to many survey reports on Java technologies (like this one of JRebel from 2020: http:// mng.bz/N4V7; or this one from JAXEnter: http://mng.bz/DK9a), Spring is the most used Java framework today.