Bits

Bits is the currency used in Equestria, and has the appearance of small, round, gold coins with an indention in the center.

Usually the money is only Applejack's problem in the first season as she needs it the farm and Granny's hip, which is discovered when she sang about it in The Best Night Ever.

Trivia

 * A "Bit" is a common colloquial term for certain coins, but it also refers to the mouthpiece on a horse's bridle.