What is a container?
A container is a directory that holds files controlled by a specific set of rules. For example, you might have your company policies stored in a container. It would be assigned a set of rules to enforce revision control with required approvals. Another container might hold the time sheets for your company. This would have a different set of rules assigned to it but would still be called a container.
A Container is a way to put together a lot of small files into one larger file to improve performance. This works very well with resources that include tapes (such as HPSS). The whole container is retrieved from tape, cached on SRB disk, and then multiple files can be quickly read and written on the container copy on disk. The SRB handles the book-keeping for the container.