Here is an example from a data-sheet of an opamp:
(At TA = +25°C, RL = 10 k connected to mid-supply, VCM = VOUT = mid-supply, unless otherwise noted. Boldface limits apply over the specified temperature range, TA = –40°C to 85°C, guaranteed by characterization and/or design.)
Does mid-supply mean ground for dual-supplies? And what does it mean for a single supply opamp?