Enterprise value can be thought of as a private market valuation for the company. When a buyer purchases a company in the private market, he has to pay for the company equity (including common stock, preferred shares, minority interest, etc), he has to pay off all the debt, but in return the buyer gets the cash the company has in its bank accounts and other cash equivalents in form of securities and other liquid assets.
Therefore, Enterprise Value can be expressed as
Enterprise Value (EV) = Market Value + Preferred Stock + Minority Interest + Debt – Cash and Cash Equivalents
In many ways, the Enterprise Value indicates the true value of the company better than the market value (which refers to just the common stock part of the capital structure).
Another thing value investors look out for are the companies that have a negative enterprise value. As you can see from the equation, this is possible if and only if the company has more cash on the books than the sum of its equity (all variants) and debt. Or put in other words, this company can be purchased in its entirety for no money at all. In fact, you can take the cash on the company books, pay off the creditors and you will have enough left over to pay yourself back and some more. Finding a company like this is quite rare but is considered one of the holy grails of value investing.