In an MS Project environment, the remaining work is how much time is needed until a task is done, or how much time is needed until a resource finishes all his work on the a project.

The remaining work is expressed in either hours or days.

For example, if the remaining work of a task is 3 days, then this means that the task needs 3 days to get done.

If the remaining work of John (or resource a) is 40 days, then this means that John still has 40 days of work on the project (the 40 days don't have to be contiguous).