Definition – What does Tick mean?
A tick is the smallest unit of time between two currency trades. Ticks are not a consistent unit of time. For high-volume currency pairs, there can be many ticks a second. For more exotic, low-volume pairs, a single tick may last for minutes or even hours.
ForexTerms explains Tick
A tick is frequently confused with a pip because, in non-forex markets, a tick has the same meaning as a pip. In forex, however, a tick is just the time that elapses between trades. Because prices don’t move one pip at a time, a tick can be worth several pips. That is, the price can fluctuate by more than a pip between each trade.
As mentioned above, ticks are relative to the currency pair and the volume of trading it sees. There is no consistent measure of a tick that can be applied across the forex market, whereas a pip is always 1/100th of 1%.