What it is
Bollinger Bands widen and narrow with how much a stock's price varies. Keltner Channels are set by its average true range, which is its typical daily move. Most of the time the Bollinger Bands sit outside the Keltner Channels. When the price stops varying enough, the bands move inside the channels. The stock is then in a squeeze. It is trading in a tighter range than it normally does, and the move out of it tends to be sharp.
How Breakaway uses it
The SQUEEZE check fires when the 20-period Bollinger Bands are inside the Keltner Channels. It counts on the finished day: during the session it keeps the last close's answer. It is a tight-range check and one of the four predictive checks called out on the card. This is a different thing from a short squeeze. The scanner shows that one separately as the Squeeze setup badge and list. That one is about short interest rather than volatility.
How to read it
A squeeze alone does not point up or down. The classic play is a squeeze inside an uptrend with volume drying up, then a first close above the prior high, with volume expanding.