"Cylinder 3 misfire detected" is the count of firings in cylinder 3 that did not produce the power they should have. Like the rest of the P0301 to P0312 range it names one cylinder by the engine computer's own numbering, and it is filed separately from P0300, which is the same count when it is spread about instead.
This is a standard code. It means the same thing on every make of vehicle.
The Misfire cyl 3 card carries that cylinder's live count, and the Full scan's per-cylinder table puts it beside every other cylinder for the last ten drives and for this drive. The Inspection screen separately reports whether the misfire monitor has run to completion since the codes were last cleared.
The Dashboard's Misfire count cards show one counter per cylinder once the engine is running, next to the Engine speed and Ignition timing traces. The Full scan's On-board self-tests give each cylinder's misfire count for the last ten drives and this drive with its share of the total, and a recorded drive works out a misfire rate over that recording for the Analysis screen and the printed report. The Inspection screen shows whether the Misfire detection monitor is done or still running.