Virtual Ground is a cero reference but without current. That is the case of the op-amp with very high gain
the opamp equation is: Vo = A(V+ - V-)
V+ - V- = Vo/A but if A = ∞ . . . . . . . . V+ - V- = 0, V+ = V-, a short circuit and because Rin is very high there is no current. That's why is called virtual because there is no current.
Floating in a circuit means that there is no conection to ground, for example the car electronics circuits. Another example is when you declare that your load is a resistor and none of his pins are conected to ground.