Just as a pip is the smallest price movement (the y-axis),
a tick is the smallest interval of time (the x-axis) that
occurs between two trades. When trading the most active
currency pairs (such as EUR/USD or USD/JPY) during peak
trading periods, multiple ticks may (and will) occur within
the span of one second.
When trading a low-activity minor cross pair
(such as the Mexican Peso and the Singapore Dollar),
a tick may only occur once every two or three hours.
Ticks, therefore, do not occur at uniform intervals of time.
Fortunately, most historical data vendors will “group”
sequences of streaming data and calculate the
open, high, low, and close over regular time intervals
(1-minute, 5-minute, 30-minute, 1-hour, daily, and so forth).