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.
This expression is the evolution of the phrase 'carpe diem' ('seize the day'). It is used to inspire courage and bravery, or to justify doing something idiotic and embarrassing. You will see YOLO spelled with its four letters, as well as with the pound sign hashtag '#YOLO'.