This defines market making as HFT, and while many HFTs make markets not all market makers are HFT. You can, using absolutely no knowledge of an underlying stoc

This defines market making as HFT, and while many HFTs make markets not all market makers are HFT. You can, using absolutely no knowledge of an underlying stock and the mathematical skills of a bright ten year old, make markets manually. In 2015, if you do it in a highly-traded U.S. equity, you probably will not have a great risk-adjusted return because your bright ten year old is in all ways worse at this task than a computer is, but it is very doable. To the extent that HFT is more meaningful than Big Data ("trading that I don't like and data I think is valuable, respectively!"), it had to include some element of Very Frequent, Very Fast. How fast? Like "the speed of light is literally a logistical challenge fast." If you see an order in Chicago and make an order in Tokyo a second later, no matter what your rationale is, you are not doing HFT. That's just T. Got a model of the mind of your counterparty? Oh, welcome to T. Observed a correlation in an ETF and its underlying stocks and using it to trade with 1,000 times a minute? Wow, such impressive T!