Tick is the term used to indicate the minimum price movement in a given security.  It is known as the minimum price change.  For example, the ES futures contract trades in 0.25 increments.  Each 0.25 is one tick. 

The tick value is the cash value of one tick (one minimum price movement).   For example, again using the ES futures, each 0.25 is valued at USD 12.50.  So the tick value for the ES futures is USD 12.50.