What is the Spring IoC (Inversion of Control) Container?

The IoC container is the core of the Spring Framework — it's responsible for instantiating, configuring, and managing the complete lifecycle of application objects (beans), based on configuration metadata (annotations or XML). Instead of your code creating its own dependencies with `new`, you declare what a class needs and the container 'inverts control' by injecting them for you, which is the foundation Spring's dependency injection is built on.