Question:

What does "fill the gap" mean?  Does it mean it has no support there?

My Response:

It’s a good question.  Filling a gap  occurs as the gap fails to ignite further excitement to push the stock even further.  Traders
see the lack of conviction in the gap and take profits and/or sell short.  Another important thing to consider is that specialists on the NYSE  and MM’s on the the Nasdaq are trying to make money too.  They see a surge in overnight buy orders (leading
to the gap up) and try to pump the stock up further by buying shares themselves.  Some investors see the gap up with a surge in volume and jump in due to greed.  But the specialists know better and begin dumping their shares for a nice profit.   It’s fairly common to see a stock fade a bit after a gap up and find support at the price where the gap started (this is filling the gap). Stocks that continue higher throughout the day and into the next couple days are showing tremendous strength.  Two things to note on AUO in this situation.  Notice that on the day the stock gapped up, that volume was below average.
That was a clue that the rally probably wasn’t sustainable.  The volume in the morning was nearly double the average (by checking the hourly volume)… but it clearly fades  into the close (even though the price surged).  The next day it fills the
gap and finds support at the price where the gap started on lower volume, which was a good sign.  However, it didn’t hold support there after filling the gap and tanked today on very large volume.   The action in AUO in the last few days has definitely been the result of the election.. it was widely believed that the opposing candidate was going to win the election, which
many thought would be best for the Taiwan market.  This resulted in the gap up.  This didn’t happen and the stock as well as the Tawain market took a hit.  The bounce off of the 35DMA was encouraging, but it’s best to wait for the dust to settle.  Sorry for the long rambling explanation.. short on time.  Let me know if i’ve completely confused you!  i’m good at doing that.