Definition & Meaning of "dressed (up|) to the nines"

What is the origin of the idiom "dressed to the nines" and when to use it?

The origin of the idiom is uncertain, but it is believed to have originated in the late 18th or early 19th century. The phrase "to the nines" is thought to be a variation of the earlier phrase "to the eyes," which means to the highest degree or to perfection. "Nines" may have been used as a metaphorical way to express the idea of excellence or completion. "dressed to the nines" is typically used in a positive and admiring manner to describe someone's appearance, particularly when they are wearing formal or elaborate attire.