A "flickering" order is one which is repeatedly submitted and cancelled (whether it's at the top of book or not).
The answer from @chollida mentions that "the goal typically is to either slow down competitors quotes by flooding the gateway interface with noise" but I don't think that's necessarily true.
Rather, I think many flickering quotes are caused by an unintended feedback mechanism - the trader submits an order, thereby changing the displayed order book. Their model processes the new book and tells them to cancel the order, which they do. Now the book looks the same as it did previously, and their model tells them to submit a new order, etc etc.
The solutions are typically -
- Hard-coded rules to not repeatedly submit and cancel orders in a short period of time, or
- Filtering the order book so that your model does not process your own orders.
Not all firms do either of (1) or (2) and so they will accidentally quote flicker from time to time.