For your typical "hodler", a dip is simply just a drop in price. I'm sure only a very small percentage of the "hodlers" are actually decent traders, so if someone says "buy the dip", then chances are, the person just said it just because the price dropped a certain percentage. Always remember that bitcoin and the cryptocurrency markets are hugely unregulated, so expect a lot of amateur "investors" in this space. Not to mention that "buy the dip" is also being used as a meme nowadays since the bear market started, when people thought price $x was the floor, but it continued to drop lower. Buy the dip!
So refreshing actually having a good well-thought question here in Bitcointalk.
I think people miss used the dip just like what you just said show how you understand the dip in trading, the dip is when there is a crash in market with a very big percentage which has giving a chance to buy less with what was before even at times x2 of what you suppose buy and hold for long time but many see every slid in price as a dip which is totally wrong and bottom is when you see that all level of any chart you use is extremely at the bottom of the chart and no other way to move up even if its 10-20% and resell to see another bottom but some see it as just $1 drop then it is dip .