The Delta he is using is the difference between market buy orders vs market sell orders. If there are 128 market buy orders on a bar and 57 market sell orders the Delta of that bar is +71. Delta is essentially market imbalance. There is even a platform called "Marketdelta".
Keeping an eye on the delta can be useful for trading; particularly divergence from price.
I found an old webinar presented by fulcrum trading. The guy only trades the FX futures from what I saw. I read some reviews and it seemed like not many people had bad things to say.
I don't know WHY you would pay any money to take a class when it is seems like something you could learn on your own. Just put up a delta bar chart under your regular chart and look for divergence. It is something I watch; it's useful to me.
I actually use volume on 2 counter-trend signals, one looking for divergence from one downclose bar to another downclose bar, not the lows or highs. But I only take these trades when market has gone into zones I expect reversals. But if size of bars are greater than 2 points, I use secondary entry of I call yo-yo, wait for breakout then retracement so I don't have to risk more than 2 points. ES has waves within a swing, so when bars are half or more of size of a wave, very good chance it will retrace.
Still think "Delta" advertising fancy word for "net", the only difference I have seen on nearby bid/ask quantity is the first one down to zero, it is next price level, traders don't realize in nano second how much volume they don't see on the Dome, there is one pattern I watch for when coming up to longer term trendline or previous strong pivot highs/lows, watch to see if volume increases or dries up, if dries up am expecting running of the stops and reversal and if more quantity then I expect going through that area.
I think vendors want to be able to come as close to "Delta Phenomenon" without infringing on that overly expensive four bar pattern. https://www.deltasociety.com/product/delta-phenomenon