This is used in different contexts.
If you are looking at a set of accounts, it refers to the sales (or revenue) figure. If, on the other hand, you are using it in the context of share trading then it refers to the volume of trades that have been executed during a particular trading session. High turnover is usually a good sign in a rising market in that it suggests that the bullish price trend is backed by a high number of deals. Trends that are observed on the back of low stock turnover may not be as reliable.