"Slam"--what is it, is it really accurate?

I put this question under speakers because I assume "slam" is mostly a function of the speakers, but perhaps a certain level of amplification is required. The only places I have experienced slam is listening to certain demos at audio shops, and some live music. Most speaker demos I have heard over the years did not produce slam.

So, what mostly accounts for a system producing that "slam" you can feel in your chest? Is it that certain speakers are "voiced" with a mid-bass hump that causes it? Do they EQ the signal to produce it? Do they employ super powerful amps?

Secondly, how accurate is slam? How much of a goal in speaker selection should the ability to produce slam be?

The reason for the questions is that I am getting close to being in the market for new main speakers. My current amp is a McCormack DNA 1, BTW. Thanks for any info!