Walking is a sequence of steps, each step being taken by an alternate leg. A single step can be broken down further into the placing of a foot on the floor (called a foot placement) and the movement of weight over that foot (called a weight transfer). The complete transfer of weight onto that foot leaves the other foot free to move, so the walker has no choice as to which foot to use next.

So, a foot placement followed by the full transfer of weight (a definite step) will ensure that you use the other foot next. This concept holds the key to dancing effectively, because in salsa and merengue, the legs are also used in alternation. Proper control of your weight transfer gives you proper control over your dancing. If you can walk, you can dance.
 

Definitions

Step: a foot placement followed by a weight transfer over that foot.

Foot placement: selection of a particular spot on the floor and the movement of the foot onto it.

Weight transfer (also known as a weight change): a shift weight from one leg to another.

Complete weight transfer (also known as full weight transfer): a shift of weight so that one leg bears all (100%) your weight.

Partial weight transfer: a shift of weight so that both legs bear a part of your weight.

Tap: a foot placement without a transfer of weight over that foot. Try standing with your weight on one leg, and tapping the floor with the other. Be aware that tapping the floor too hard encourages a partial transfer of weight over the tapping foot.

Replace (short for replace of weight): moving your weight to where it was just a moment ago. Strictly speaking, after a step is taken, the free foot remains where it is (in place) on the floor and weight is moved back onto it.

The tap and the replace are related: the tap is a foot placement without a new weight transfer; and the replace is a weight transfer without a new foot placement.

Null beat: A beat in the rhythm that is not "used". For example, in salsa there are four beats per bar of music: three dance beats and one null beat. Steps are taken during each dance beat, and no steps are taken during null beats. This results in the step–step–step–wait pattern of the basic salsa. In contrast the merengue has no null beats in its basic pattern and has a step–step–step–step pattern. This is similar to walking making merengue an easier dance to learn.

Highlight (also known as an adornment): Some dancers get bored during the null beat so they decorate it with a highlight. It can take the form of a tap, a flick of the foot, and so on. The options are endless. The salsa pattern would then change to e.g. step–step–step–tap, or step–step–step–flick. While the use of adornments can contribute to the visual appeal of the dance, it's important to remember that it is only supplementary to the structure of the dance.