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 'yo-yo'. Word Frequency. yo-yo (joÊ joÊ ) Word forms: plural yo-yos. countable noun. A yo-yo is a toy made of a round piece of wood or plastic attached to a piece of string. You play with the yo-yo by letting it rise and fall on the string.