Asset value is one way investors measure what a company is worth: add up everything it owns and subtract everything it owes. The result is more often called book value, which is explained in full, with the formula and a worked example, on that page. It is read from the company's balance sheet.
For an investment fund the same idea, worked out per share each day, is the net asset value (NAV). Analysts compare asset value with the share price to judge whether a stock looks cheap or dear.