[gijoe9]

As my friend has mentioned volume of a particular stock is the number of shares that traded that day. The average volume will be the average number that trade per day (averaged over the last ninety days usualy). It is important to note that volume plays a part in numerous ways when trading. If the volume is 50 million on a day does that mean that 50 million different shares changed hands? Some shares may change hands several times in one day but all trades count toward the volume.
Thinly traded stocks (low volume) are hard to get into and out of sometimes. Hard on the way in because it will cost you more then the current share price and out because you will get less than the current share price. Stay away from these til you get a better understanding of volume and how it effects trading. Generaly you will get the market price on high volume stocks when you buy or sell.