Prince

A prince is a title that is often, but not always, reserved to the children of Kings and Queens, but in rare instances may be equal to a king. The role of princes tend to vary depending on the region and culture, but are often well-respected or highly revered. Its feminine equivalent is princess.

My Little Pony
Many princes, mostly humans, appeared throughout My Little Pony and its comic book, most of which were humans. Some of the more notable princes include Prince Philip and Prince Edgar. With the exception of Prince Philip, most princes were the children of monarchs, while Philip himself seemed to be the ruler of his land.

Tales
Squire was the prince of an ancient kingdom, though he desired to be a knight and thus decided to slay the evil Bazzle, who took his life.

Friendship is Magic
Some of the oldest known princes include Prince Hisan and Prince Blue Dream, respectively.

Despite how princess is synonymous with queen in the land of Equestria and beyond, the role of prince varies significantly. While Prince is highly respected as co-ruler of the Crystal Empire, other princes such as  do not appear to have much power. By contrast, the title of prince appears to be the equivalent of king among the yaks of Yakyakistan, whereas it is subordinate to king in the Kingdom of Thicket and the Infernal Lands.

Equestria Girls
In Canterlot High School, the term "prince" has been used to describe the Fall Formal Prince, the young man who wins the Fall Formal.

My Little Pony

 * Prince Edgar
 * Sir Hugonaut
 * Prince Berin
 * Prince Philip
 * Prince Rudolph
 * Prince Hal
 * Prince Cal
 * Prince Tal
 * Prince High
 * Prince Valiant
 * Prince Edgar
 * Prince Edgar

Tales

 * Squire
 * Prince (The Nutcracker)

Friendship is Magic

 * Prince Abraxas (Farasi)
 * Prince Aello (Ornithia)
 * (Equestria)
 * Prince Blueblood (Deviations) (Equestria (Deviations)-formerly)
 * Prince Bluebeard
 * Prince Bluebottle
 * Bramble (Thicket)
 * Prince Crompus (Yakyakistan-formerly)
 * Prince Dromius (Yakyakistan-formerly)
 * Prince Drutherford
 * Prince Fancy Pants
 * Prince Gruntwig (Yakyakistan-formerly)
 * Prince Hisan (Somnambula)
 * Prince Rutherford(Yakyakistan)
 * (Infernal Lands)
 * (Crystal Empire)
 * (Infernal Lands-formerly)
 * Prince Ulysses (Yakyakistan-formerly)