Physics, Chemistry. 1  a wave function describing the state of a single electron in an atom (atomic orbital) or in a molecule (molecular orbital) 2  the electron in that state.
DEFINITION of 'Yo-Yo'. Slang for a very volatile market. A yo-yo market will have no distinguishing features of either an up or down market, taking on characterstics of both. Security prices in a yo-yo market will swing very high to low over a given period of time, making it difficult for buy and hold investors to profit. Next Up.
Definition of yoâyo. plural. yoâyos. 1 : a thick grooved double disk with a string attached to its center axle that is made to fall and rise to the hand by unwinding and rewinding on the string. 2 : a condition or situation marked by regular fluctuations from one extreme to another. 3 : a stupid or foolish person.