A tick is a measure of the minimum movement in the price of a security which can be either upward or downward. It can also refer to the change in the price of an instrument from one trade to the next trade.
Tick history, or historical tick data as it's often called, is a list of all ticks for a selected instrument at a certain point in time. A comprehensive tick data download can provide invaluable insights for traders and analysts alike, as it includes the full spectrum of price movements over a given period.