Noun: Generally a small, raggedy place (usually a bar or a club) that has very low quality equipment, furniture, etc but sometimes will provide the best variety of entertainment on any given night. Defining characteristics include: holes in walls/ceilings, nonflushing toilets, a ceiling fan instead of central air, $5 "to get in", and only one bartender. Most of these types of places are found in the country and in the south.
"Man, forget all that upscale crap!! Tonite I am going to the hole in the wall!"
"I heard that the hole in the wall on the other side of town got shut down by the city because it failed the building inspection".
"If you wanna go and have a good time without getting too fresh, try going to the hole in the wall"
any thing advantageous one keeps hidden until the right moment to use it. This is a play on playing cards, in which the Ace is the highest ranking card.