Input Bias Current
The inputs should have an impedance of infinity, meaning absolutely no current flows into them. However, this is not actually the case. The amount of current that flows through the op-amp input is called the input bias current.
The input bias current is the DC current required by the inputs of the amplifier to properly operate the first stage. By definition, the input bias current is the average of both input currents.
Electronic Devices : Conventional Current Version, 9th Edition by Thomas L. Floyd