Southpark:
Ideal op amp inputs have infinite input impedance.
There's more than that to an ideal op amp:
- Infinite input impedance
- Zero output impedance
- Infinite output amplitude
- Infinite bandwidth
- Infinite open-loop differential gain
Ideal components are impossible to construct with any actual material, so all actual op-amps will be designed with different trade offs of these values and many other non-ideal parameters (input offset voltage, current consumption, supply voltage limits, noise, etc.). That is the reason why there are so many different kinds. One type might be designed to have a high AC bandwidth at the expense of lower input impedance to amplify high speed video signals. Another may trade lower bandwidth in order to have a lower input offset voltage in order to amplify very low level DC signals.