The 8-count is one of the most basic elements of learning to dance. While other counts are used, the 8-count is found in the majority of modern dance forms.
Significance
When learning or practicing dance, most songs are broken up into segments or units called 8-counts. Each of these segments is measured in counts of eight beats, or how long it would take to count out "1, 2, 3, 4, 5, 6, 7, 8" in a rhythmic fashion. Once the count of eight is reached, dancers start over from one and a new segment begins.
Function
Dancers and choreographers use 8-counts on a regular basis to learn and teach dancing because most popular dance forms are based on 8-counts, which are essentially two 4-count measures back-to-back.
Fun Fact
Even though the majority of dance styles are based around 8-count divisions, the number of counts in each segment can vary. Certain styles of dance can feature 3-count, 6-count, and even 12-count segments.