The trigger threshold — only days where volume is at least this many times the average qualify as an entry.
2× means today's volume was double the rolling average.
The number of trading days used to compute the rolling average volume that today's volume is compared against.
20 days is the most common default — roughly a month of trading.
Shorter (10) reacts faster; longer (30, 50) is smoother and less prone to one-off spikes.