Contract and share volume are used in futures and stocks, respectively. This is the precise volume. Tick volume is used in CFDs and Forex. Volume always equals activity. Tick volume is a measurement of the change in price or tick per time period observed. Tick volume has been found to be 90-95 percent similar to actual volume in study after study. Most traders who use volume (tick or actual) will say that the most important factor is how volume compares relative to other traders. In other words, period x's volume (tick or actual) in isolation does not have the same significance as period x's volume (tick or actual) in relation to period x-1's volume (tick or actual). So, no matter what type of volume is being considered, the key is to compare it to others. The term liquidity refers to structural barriers as well as the number of, or lack of, market participants. Because there are so many traders to trade with, liquid markets are simple to enter and exit (or against). Professionals typically trade only in liquid markets because they take large positions and do not want to bid up or bid down the price against themselves in low-volume markets. This is why the E-mini futures contract is traded by more professional traders than the rough rice contract.