Book Value - or Net Asset Value - is a measure of shareholder's equity and is calculated as Assets less Liabilities and any Preferred Stock.

From the accounting perspective, it could be seen as the underlying value of a company, whereas the market capitalisation value is dictated by the supply and demand of shares.

However, should the company go into liquidation, the Book Value is often used as a proxy for the value remaining for common shareholders after all creditors are paid.

This is measured on a TTM basis.