Book Value - The amount something is worth. This may or may not be equal to the actual value of the item. The Book Value is calculated by taking the original value of the item (what you paid for it) and deducting any depreciation which you have taken on the item.
Example:
You purchase a truck for $100,000. At the end of the first year you take a $25,000 deduction for depreciation, the current book value of the truck is now $75,000.