In the electron cloud model of the atom, an orbital is defined as the most probable of what?

On orbital is where the electrons are located, and the last or outer orbital is where the valence electrons that determine the properties are located. 

The  grandmother cell  is a hypothetical  neuronthat represents a complex but specific concept or object.[1]  it activates when a person "sees, hears, or otherwise sensibly discriminates"[2]  a specific entity, such as his or her grandmother. the term was in use at least as early as 1966 amongst staff and students in the department of experimental psychology, university of cambridge, england. a similar concept, that of the  gnostic neuron, was proposed two years later