"So What Exactly Is Dance?"
Dance (from Old French ‘dancier’) generally refers to human movement either used as a form of expression or presented in a social, spiritual or performance setting. (www.oed.co.uk)
Dance and It's Origins
It is impossible to say with conviction when exactly dancing became part of human culture. However, dance has certainly been an important part of religious ceremony, rituals, public celebrations and of course entertainment since the earliest human civilizations were formed. Archaeology delivers traces of dance from prehistoric times such as Egyptian tomb paintings depicting dancing figures from circa 3,300 BC and the Bhimbetka rock-shelter paintings in India.
One of the earliest structured uses of dance may have been in the visual performance aspect of retelling mythological stories passed down by group elders. Indeed, before the introduction of written languages, dance (and speech) was one of the primary means in retelling these stories through generation and generation.
The early use of dance was more than likely invented as an antecedent to ecstatic trance states during most healing rituals by early medicine men. Dance is still used for this purpose by small tribal cultures from the Brazilian rainforest to the Kalahari Desert. Many contemporary dance styles can be followed back to historical, traditional, ceremonial, and ethnic dances of the earliest human cultures. Have you ever heard of a ‘rain-dance?’

An African Rain Dance taking place.
Dance and Music
Dance and the Drum go hand in hand. Dance works with the drum and percussion in order for the body to move to a beat.
Although dance and music can be traced back to prehistoric times, even the best of us are still unsure of which art form came first. Similar to the chicken and the egg puzzle as to which came first, so too does dance and music continue to baffle scientists today. However, as rhythm and sound are indeed the result of movement, and music does more than often inspire such movement, the relationship between the two forms has more than likely always been a symbiotic one.
Many early forms of music and dance were created and performed together. This paired development has continued through the ages with dance/music forms such as: Jig, Waltz, Tango, Disco, Salsa, and Hip-Hop.
Although dance is often paired with music, they can both be presented independently of each other or dance can even provide its own accompaniment such as the percussion form of tap dancing. Dance presented with any form of music may or may not be performed in time to this music depending on the style of dance that is performed. Dance presented without music is said to be danced to its own rhythm and indeed tap dancing does hold up its own rhythmical values.

Famous Dance artists Fred Astaire and Gene Kelly often provided their own dance percussion.
The Study of Dance
From as early as the 1920s, dance studies, dance practice, critical dance theory, the analysis and history of dance began to be considered as an academic discipline and much more than just an art form. Today, dance studies can be seen as an integral part of many Universities' Arts and Humanities degree programs. By the late 20th century the recognition of the practical knowledge of dance was as equal to the academic research practiced on other subjects such as molecular-physicals and practical mathematics.

Dance is now an intergrated University subject.
Competetive Dance
While many people view this style of dance as a recreational activity, it is becoming more often viewed as a sport. Like other athletes, dancers must be in good physical condition. Dancing requires strength, stamina, and flexibility. Competition requires these physical attributes to an even higher extent. DanceSport is in fruitition and it is long overdue.
Competitive dancing requires a high amount of dedication as there may be many months spent practicing dance and developing routines without even a final result or placing in the competition. During the competition, dancers perform in front of judges who evaluate their efforts and score each routine or vote for the person, couple or team they wish to see back onto the floor for the next round. The final ranks awarded by different judges are combined into a final scoring, and medals or trophies are awarded accordingly.

A dance couple competing in a latin american competition
Each routine is required to comply with certain rules. It must enter a category which is consistent with the music, style, content, and dancers of the routine. Common limitations are: number of dancers (e.g. different categories for solos, duos & trios, small groups (4-9), large groups (10-19), and super groups (20 or more)) and average age of the dancers involved - 3-8, 8-12, 12-16, 16-21, 21-35, and 35+ Routines which fail to comply with the requirements the competition has laid out will be disqualified.
The judges at a dance competition are typically former dancers or have trained dance champions or former-professional champions. They stand in the middle of the dance floor or sit in the pit at the front of the auditorium in front of the stage and watch all of the dancers dance and then mark them accordingly. Each adjudicator has a score sheet or pad to mark who they wish to see through to the next round. When the final arrives points are evaluated and a percentage is given to find the winner of the competition. Points are awarded for different categories and the aspects that may be judged are: dedication to the rules of the dance, exact technicality and precision of figures, execution of movements, transition of movements, difficulty of routine, choreography, and / or musicality.

Blackpool and it's famous Tower Ballroom are the centre of the competetive dancing world.