General Discussion, page-310

It's a mid-point cross trade. It happens like this:

1. Customer A and customer B both trade on **promotion blocked** using the same broker.
2. On **promotion blocked** the current buy side is at $0.15 and the sell side is at $0.155.
3. Customer A submits a sell order for 20,000 shares "at market" for $0.15
4. Customer B submits a buy order for 15,000 "at market" for $0.155
5. Instead of placing both orders on the market, the broker "crosses" the overlapping quantity (15,000) of the two orders at the mid-point ($0.1525).
6. The balance of customer A's order (5,000 shares) is placed on the market at the specified price ($0.15).
7. **promotion blocked** is notified of the crossing so it goes into the course of sales.
8. Customer A is happy because they got a little bit more for their shares, customer B is happy because they paid a little bit less.

I don't trade frequently, but I've had orders crossed by my broker.