http://www.webopedia.com/TERM/L/logical_drive.html
A part of a physical disk drive that has been partitioned and allocated as an independent unit, and functions as a separate drive altogether. For example, one physical drive can be partitioned into drives F:, G:, and H:, each representing a separate logical drive but all still part of the one physical drive.
Using the logical drive hierarchy is one method of organizing large units of memory capacity into smaller units.