Slippy --
I like to describe Duration as the "window of opportunity" during which a
task will actually be performed. Duration is measured by default in working
days. Work is the actual effort expended to perform the task, measured by
default in hours.
Duration and Work can be two different values. For example, an executive
has 5 days to perform a review, but will actually work only about 4 hours to
do the review. On this task, the Duration would be 5 days and the Work
would be 4 hours. Hope this helps.