The Japanese refer to what commonly called a gap as a window. Expression like "filling in the gap" is therefore equivalent to "closing the window".

There are two kinds of windows, one bullish and the other bearish. A rising window is a bullish pattern. There is a price vacuum between the prior session's high and the current session's low.

A falling window is a bearish pattern in which there is a gap between the prior session's low and the current session's high.

It is said by Japanese technicians to "go in the direction of the window". This is because windows are continuation patterns. With the emergence of a rising window, one should look to buy on dips, and with a falling window to sell on bounces.