essentially, almost, if not all, trades are being front run by HFT (algos).
the closer you are to the data processing center for a certain exchange (the man in the video was from
BATS) (i.e. the less fiber that separates you from different exchanges), the sooner you have the real stock price ( in some instances, microseconds, in others, milliseconds). There are programs/algos written that take advantage of those of us that are not as close to the market (internet, cellular, etc.) and do not have the accurate stock price.
They use this market inefficiency to short and long stocks (holding for very small amounts of time) and profit off of those that do not have the latest information.
ie. you place a bid for 1,000 shares at 10$, the bid price is actually 9.98, so the algo buys 9.98 and sells to you at 10 for a 20$ profit in a few milliseconds. Rinse, wash, repeat.
There's a lot more to it than that, but that's the surface level to it.