An electron unassociated with any particular atom, relatively free to move through a crystal lattice structure under the influence of external forces.
An electron that has broken free of it's atomic bond and is therefore not bound to an atom
An electron that is had freely broken of him is atomic connection and therefore it is not limited an atom.
A valance electron that has broken away from its parent atom and is free to move from atom to atom within the atomic structure of a material.
An electron not bound to an atom or molecule. In this sense a (negative) beta particle is a free electron.