A gap is an area where no trading takes place. If a stock closes at $20 and opens the next day at $21.50, there is a "gap" between $20 and $21.50. No trading has occurred in that gap. There is an old adage that all gaps will ultimately be filled. That's just not true. Want proof? Go back to the 90's and look at how Amazon traded in its infancy. There are plenty of gaps that have never been (nor will ever be) filled. But gaps are very important patterns because of the obvious information they provide - no trading activity within the gap. So when a price starts to fall back into the top of a gap, it goes into a "void" - where no trading has occurred. At that point, the stock will often fill the void. These videos explain this concept in detail. Learn to trade the gaps, and you'll soon be able to stop buying your clothes at The Gap.