Measuring maximum output current of Operational Amplifier
The precise definition of that current is whatever the manufacturer means.  Usually a manufacturer will limit the output current so that a designer won't destroy parts by asking too much -- but in the case of power op-amps, or other specialty op-amps, that may not be the case.

The two most likely definitions of "maximum output current" are "this is the most you'll get with the output shorted to one rail or another", or it is "don't ever exceed this or you'll let out the magic smoke".