Trading on markets means being a buyer or a seller. In order to execute a trade, you need a counter-party, and the way most people think of that is like "you submit an order to your brokerage, which then pushes your order to an exchange and their algos find the best match for your order". This is the case indeed, but it's not the only way. There is also a thing named Dark Pool.
A dark pool is a privately organized financial forum or exchange for trading securities. Dark pools allow institutional investors to trade without exposure until after the trade has been executed and reported. Dark pools are a type of alternative trading system (ATS) that gives certain investors the opportunity to place large orders and make trades without publicly revealing their intentions during the search for a buyer or seller.
Depending on a market, the share of dark pool activity can vary dramatically: for some stocks barely any trades happen outside of public exchanges, and for some other stocks 70%+ of trading activity runs on dark pool on a regular basis.
On TrendSpider, we have this data illustrated in a way so that you can see 1 thing: what is the share of trading activity happening outside of public exchanges at a given time.
Example 1: for this stock, 50%+ of activity usually revolves on dark pool (dark area).
Example 2: for this stock, dark pool used to have barely any activity, but there was a spike in dark pool volume around Nov'21 to Jan'22.
NOTE 1: Dark Pool Volume data is of Weekly granularity (1 data point per week) and it's delayed, by 3 to 5 weeks.
NOTE 2: For Stocks and ETFs, our historical DWM Volume data does incorporate Dark Pool data as well. It was the case forever, so nothing has changed when we've released the Dark Pool indicator.