Om saravanabhavaya namah is a Sanskrit mantra that is believed to bring good luck, abundance and prosperity. It is sometimes called the Kartikeya mantra or Muruga mantra, named after two of the identities of the eldest son of Shiva and Parvati.
A mantra is a single syllable, word or phrase that's often chanted more for the power of its sound vibrations than for any specific meaning in the words. It can, however, be an appeal for the assistance of a particular deity.