It is a mnemonic phrase to help a person remember the order of the planets. My Very Excellent Mother Just Served Us Nine Pies = Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. Since Pluto has been demoted to a dwarf planet, one might choose the sentence "My very excellent mother just served us noodles."

HOMES is an example of a name mnemonic (or acronym) for the Great Lakes: Lake Huron, Lake Ontario, Lake Michigan, Lake Erie, and Lake Superior. A common example of a music mnemonic is the ABC song children sing to remember the alphabet.

There are many kinds of mnemonics and many different uses, such as spelling, order of things, math, music, and foreign language. Mnemonics even have medical use!

Mnemonics have been used for aiding patients with a memory deficit from different causes and conditions. In most cases, it is very helpful. Stroke victims, however, don't show much statistical significance.

More Info: en.m.wikipedia.org