Hi, and welcome to this forum.
You are seeing tick-volume, and it is specific to Oanda.
Ticks are price changes. They are not orders, and they are not volume in the usual sense.
Oanda’s tick-volume is simply a count of the number of times the price of a given currency pair changes in a given time period on the Oanda platform.
Here’s why we pay attention to tick-volume: The number of price changes per time period varies from one time period to the next, and this variation is roughly proportional to actual trading volume (which cannot be measured directly).
So, Oanda’a tick-volume for a given pair is a proxy for actual Oanda trading volume (which, if it could be measured directly, would presumably be measured in lots traded).
Furthermore, the tick-volume displayed by any large broker* mirrors closely the tick-volume displayed by other large brokers, and therefore it mirrors closely the actual volume of the overall (worldwide) market for a particular currency pair in a particular time period.
Consequently, by watching changes in tick-volume, we can get a good sense of the rise and fall of real volume (and of the volatility and liquidity associated with real volume) from one time period to the next, or over the course of a trading session, or over the course of an entire trading day.
* Regarding broker size: There are now only two large retail forex brokers in the U.S., forex.com (the largest) and Oanda. Forex.com is the retail division of Gain Capital, which has recently acquired the U.S. retail accounts of FXCM. With this acquisition, forex.com now has about a 58% share of the U.S. market. Oanda has less than half as much share.
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