Lognormal bell curve rather than normal bell curve?

In discussing the movement of stock prices, finance quants talk about log-normal bell curves. Can someone give me a brief explanation of why "log-normal" rather than plain ol' normal?

Stock prices can't get below zero. (Because investors in equity, as a matter of law, are protected from the liabilities.) That may be pertinent. Is log used to keep the left hand tail of the curve from getting into negative numbers?