What is a container?

I often visit the term 'lightweight container' and 'heavyweight
container' and I 'infer' the meaning from the context. In some
contexts such as EJB literature, it means a specific container class
implementing a container interface whose job is to contain the bean
(server/service).

In another context, like in the WebWork In Action book, it is loosely
meant to refer to servlets and Web servers that contain mechanisms for
handling HTTP methods.

In yet another context, during a discussion with a colleague, he used
the term to mean the general connotation of the word container. He
said, "like a company contains many employees, therefore a company
object is a container for employee(s)".

I am a Java beginner, so please be gentle on me. I have not completely
read a single book on Java except one old book on Applets. I am in the
process of reading the Core Java 2 volumes, but have not been able to
devote much time.