Maya means "that which is not." It refers to the Supreme Person's energy of illusion, which makes us think our temporary body, which is a product of the material world, is the same as our eternal, spiritual self, the atma within the body. When we're under maya's influence, the attractive things in this world—wealth, fame, the opposite sex—appear real and desirable to us. We think we should be able to enjoy and control them, as we like. But really, everything here is under the control of time, and none of these temporary things can bring us lasting happiness.
Everything about Krishna, the Supreme Person, is completely spiritual. He always has been and always will be the supreme controller and enjoyer. But when we want to enjoy or control separately from Him—as if we were God ourselves—everything then appears to us as material, non-spiritual, separate from God, and exploitable. What we see then is maya, illusion, because in reality nothing is separate from the Absolute Truth, the Supreme Person, Krishna.
(The image is a well-known ambiguous optical illusion entitled, "My Wife and My Mother-In Law." The person in the picture can be seen either as a young woman or an old woman.)