What is Spring?

Definition:
"Spring is a Open-Source, Light-Weight , Loosely Coupled and Dependency Injection Based  Aspect-Oriented Java/J2EE Application Framework."
                                     

Come To Each Word...

Open-Source:  As You Know Open-Source software  Means available at Free of Cost to Users and also Allows public to Provide enhancements and Modifications to The Software under some Licences(free).

Light-Weight: Some Components required High-End Web servers or Application Servers to Run and Resources of these components also should be implemented by Involving the component's  APIs, but

• Most of Spring  applications can run outside of web/Application servers.
• Spring supplies two light weight containers they can activate without server also. 
• The Resources of Spring Applications can be implemented without using spring API (as POJO & POJI).

B'coz of These reasons SPRING called as Light-Weight.

Loosely Coupled: If Degree of Dependency is less B/w components then those components called as Loosely Coupled components. Spring is also Loosely Coupled because of

• The Dependent Values required for Spring Application can be supplied from out-side of app Through Xml files & Properties Files.
• We Can Use Spring Modules Individually or Together in Application Development.
• We can Integrate Spring other Java, JEE Technologies and F/Ws in Project Development. 

Dependency Injection: If The Underlying Technology or Framework or Servlet or Run-time Environment is Dynamically pushes/assigns dependent values to the resources  even though  they are not satisfying any contract, then is is called Dependency Injection. This approach is also called  Inversion of Control.

Aspect-Oriented: Spring is Aspect-Oriented Because it provides Provision to Apply Aspects/Middle ware Services on Spring Application.
Spring allows us to apply middle ware services through Spring Aop Module, Aspectj.