Suspension is a weight transfer technique using the calves muscles so that the vibrations from the steps are not transferred into the dancer’s body. The term is coined from a car’s suspension, which absorbs the shocks from the road so you do not feel them while driving.
The 1st video illustrates the ultimate suspension, which is Michael Jackson’s moonwalk. Notice the dancer looks like as though he is skating on ice. This is a common effect in social dancing videos of the pros, as their lower body is usually cropped off during filming, yet they look like they are skating on ice.
The 2nd video is an example of the opposite, the lead in this video does not have any weight transfer and notice how the vibrations travels up his form.
To practice suspension, the lead must learn how to insert the intermediate positioning of the steps. Similar to the how to moonwalk video the lead must engage the calves to eliminate any bouncing motion. This is also known as toe to heel and it should be covered in the intermediate salsa class. Suspension is a concept for leads but applies to follow as well. The difference is that suspension is enforced if the follow is wearing heels. This is why it is very rare for the follow to develop the "lazy foot" as the calves are engaged implicitly.