Define input current of Op-Amp
Well spotted! There is an input current, but it can be really small. It's usually specified as "bias current" in the datasheet. For older parts it'll be some number of microamperes. For specially designed JFET inputs for instrumentation amps, it can be as small as femtoamperes, which are really hard to measure. (The part mentioned is the LPC662 which claims 2fA input current!).

For normal analysis purposes you ignore it, but it can matter when you're trying to amplify a small signal.