An 'imaginary' measure of how much each shareholder would receive if the company terminated its operation, settled all its debts, and ended up with a cash balance available for distribution to shareholders. A comfort factor for investors about the underlying asset strength of a business when considering investment.
You are about to buy shares in a company, when a devil appears at your shoulder and whispers 'They don't have any assets, it's all fresh air.' Companies may be profitable and have very few assets. Companies also may make losses yet have billions of dollars in assets. Assets in cash value less losses, all divided by the number of shares in circulation, determines the Net Asset Value per share.