What a tick is
A tick is the smallest unit of market data: a single update marked with the exact time it occurred. Each tick carries a price and a size and indicates either that a quote changed or that a trade took place. In sequence, ticks form a complete, moment-by-moment record of how a market moved, with no detail removed.
Tick data versus OHLCV bars
Ticks and bars sit at opposite ends of the detail spectrum. An OHLCV bar condenses an entire interval into five values, which is compact and easy to chart but omits the sequence of events. Tick data retains every update, preserving the exact order in which events occurred. Many systems store ticks as the source record and aggregate them into bars on demand, since bars can always be built from ticks but not the reverse.
Quote ticks and trade ticks
Tick data generally divides into two streams. Quote ticks record changes to the bid and ask, capturing shifting intentions to trade. Trade ticks record executed transactions, capturing completed activity. Both are ticks, but they answer different questions, and many feeds allow subscription to one, the other, or both.
When tick-level detail is required
Tick data is most valuable where the order and timing of events matter: reconstructing how a movement unfolded, measuring fine-grained timing, or backtesting strategies that respond to individual updates. The cost is volume, as an actively traded symbol can produce thousands of ticks per second, which increases bandwidth and storage requirements. Where analysis can be performed on bars, the full tick stream is generally unnecessary.
Ticks on SiftingIO
SiftingIO streams a canonical price tick over WebSocket under one schema for every market, so the live edge of the data arrives update by update rather than as periodic snapshots. OHLCV bars and derived metrics can be computed from this stream with full control over the method, while historical bars are available over REST where tick-level detail is not required.