146c5814_What_is_an_Ideal_Op_Amp___Ideal_Op_Amp
[Characteristics] Infinitely high input impedance [Real Op Amp] A real op amp has finite input impedance. Even though many types of op amps, such as MOSFETs, have extremely high input impedance, in the order of teraohms, it is still finite. [Ideal Op Amp] 
An ideal op amp will have infintely high input impedance. This will ensure that the op amp causes no loading in the circuit. The lower the input impedance, the more current that an op amp will draw. The higher the impedance, the lower the current that an op will draw. We want high input impedance so that the op amp doesn't disturb the original circuit by pulling current from it. To do this, we need infinitely high input impedance.
What is an Ideal Op Amp?
Ideal Op Amp