|“The fundamental unit of information in quantum computing (called a quantum bit or qubit), is not binary but rather more quaternary in nature, which differs radically from the laws of classical physics.”
Casey Kazan, The Quantum Future of Computing
A qubit can exist not only in a state corresponding to the logical state 0 or 1 as in a classical bit, but also in states corresponding to a blend or superposition of these classical states. In other words, a qubit can exist as a zero, a one, or simultaneously as both 0 and 1, with a numerical coefficient representing the probability for each state. This may seem counterintuitive because everyday phenomenon are governed by classical Newtonian physics, not quantum mechanics — which takes over at the atomic level.
Good explanation of quantum computing here from Cosmos Magazine.