Referring more generally to the Container pattern (of which an enterprise Java container could be considered a specialization), the book Server Component Patterns by M.Volter, et al. offers the following:
[A CONTAINER provides] an execution environment that is responsible for adding the technical concerns to the COMPONENTS…Conceptually, it wraps the COMPONENTS, thus giving clients the illusion of of tightly-integrated functional and technical concerns.
Examples of such technical concerns include security, transaction management, logging, etc.