Stock price when the opinion was issued
Basically the NASDAQ 100. Acts as a benchmark for a lot of people like himself. Extremely liquid. Trade, rather than invest. Top was around $550, and he thinks it will probably take out those highs before the end of the year.
Based on the look of the chart, he'd write calls against it with a strike of around $530-540. This way, you collect some premiums. If you don't want to get taken out, just keep rolling the strike price up.
He uses the QQQ in 2 ways -- for trading and for hedging. The SQQQ is a short on the QQQ -- useful for Canadian platforms that don't allow you to get into futures and options on futures.