Tick volume
The number of price changes (ticks) in a period, used in forex as a rough proxy for activity because real traded volume isn't available.
Since forex has no central exchange reporting traded amounts, many platforms show tick volume instead: how many times the price updated during a candle. The idea is that busy markets produce more quote updates than quiet ones, so tick volume often rises and falls with real activity.
It is a proxy with known limits. Tick counts depend on the data provider, and two feeds can show very different numbers for the same candle. A flurry of small updates in a thin market can look like activity with little trading behind it. And tick volume says nothing about direction or order size.
Used carefully, it can still hint at when a session wakes up or when a news release hits. Traders who rely on it usually compare it with its own recent average rather than reading absolute values.
Sky Trade's feed has no volume of any kind, tick volume included, so none is shown on the chart. On OTC instruments ticks arrive every 0.5 seconds from the server's model, so counting them would tell you nothing anyway. For the bigger picture, see volume and volume basics.
On a feed that provides it, an M1 EUR/USD candle at 03:00 UTC might show 40 ticks and one at 13:30 UTC, right after US data, 600. The jump reflects activity, not the amount of money traded.