Spring is a module based open source framework to build robust Java / Java EE applications.
The core feature of the Spring framework is its Dependency Injection and Inversion of Control. Beside this feature Spring provides several modules to extends its feature richness.
This tag should be used when your question is related to the usage of the Spring framework and its APIs and techniques. As Spring has a broad range of sub-modules you should consider to use a more specific tag if you have a question to one of this sub-modules. For example if your question is about the MVC module then you should use the spring-mvc tag too. To avoid unneeded callbacks to your question ensure to make clear which version of Spring you are using.
Before posting a question you should at least read the introducing of the Spring reference documentation as it gives you a good summary about the framework. Also you should read the section about the core technologies.