Excerpt from "The Reel" from English, Welsh, Scottish & Irish Fiddle Tunes by Robin Williamson
"The reel is still the most popular form with Irish and Scots traditional players. The Irish play the reel very briskly and lightly, all melody and rhythm with much ornamentation and an accent on virtuosity. The Scots play the reel a little slower than the Irish and their tunes are more chordal in structure. The Scots reels often feature a characteristic modal chord change of a whole tone: i.e., from A down to G and back again. This gives the music a rather craggy and warlike feel. Nowadays the reel is most commonly danced by groups of eight."
Reels are commonly danced by traditional Irish dancers. It is a softshoe dance, which is one of two softshoe dances performed in championship competitions. The reel is a currently a very athletic dance, performed by both male and female competitors.
Drowsy Maggie is an example of a reel: