Tangible Book Value is an estimate of liquidation value where intangible (or soft) assets are excluded from net assets.
Tangible Book Value is sometimes used as a proxy for liquidation value - it involves deducting all intangible (or soft) assets from net assets.
As a liquidation valuation, it estimates the amount of money that a company could quickly be sold for, if it were to go out of business but it is not as conservative as NCAV or NNWC. It may be necessary to go further, for example, by marking certain assets to market.