Understanding the Texas Instruments CD4075 datasheet table
The specification is letting you know how much current the output can provide. With a 4.6 volt output the maximum current that can be drawn at room temperature is 1 ma.  If you try to draw more current the output voltage will drop.  At an output voltage of 2.5 volts, the maximum current that can be drawn, again at room temperature, is 3.2 ma.