This ratio is calculated by dividing the latest Price Close by the company's Tangible Book Value per share. Tangible Book Value per share is defined as Shareholders Equity less intangible assets.
Theoretically, PTBV represents the hard assets of the company, i.e. the amount of money that shareholders would receive for each share owned if the company were to liquidate its operations. Some 'intangible' assets can have questionable value - for example a company might have overpaid for an acquisition and conservative value investors sometimes prefer to remove them when valuing a company.
A higher PTBV may indicates a higher level of risk due to increased potential for share price losses. However, tangible book value may be substantially different from market value, especially in high-tech, knowledge-based and other industries whose primary assets are not tangible.