You have to understand a bit about how these testers work. They put a light across each pair of wires. Depending on the results, the message is one possible explanation, but further research is needed when you find a problem.
There is no standard, so using the linked Ideal tester:
- Left = Neutral/Ground - This should not be on.
- Middle = Hot/Neutral - This should be on.
- Right = Hot/Ground - This should be on.
So what does "Hot/Ground Reverse" mean? It means there is a circuit (voltage, so current flows) between neutral and ground (bad), between hot and ground (good) but not between hot and neutral (bad).
The simple explanation for this is that literally the hot and ground wires are swapped. Because then left = Neutral/Hot on, middle = Ground/Neutral off, right = Ground/Hot on.
However, wires don't just jump around within a receptacle. Either the wires have been wrong since the last time work was done on this receptacle (or possibly another junction in the circuit) or something else has gone wrong.
The solution is to:
- Turn off the breaker controlling this receptacle. All the lights in the tester should go off.
- Open the receptacle and see how the wires are connected. Note that you may have one cable/set of wires or two (or sometimes more). You may find obvious problems, with obvious fixes, or you may find nothing wrong at all (the problem is earlier in the circuit) or evidence of serious problems (e.g., arc damage).
Similar for Hot/Neutral Reverse.
The consequences can be quite serious. An actual Hot/Neutral reverse, with nothing else wrong, is not in and of itself a big deal (usually), though it should definitely be fixed. On the other hand, a Hot/Ground reverse is a major problem as it means your ground wires are carrying current, which is not a good thing.
Knowing there is a problem, I would not use the receptacle at all until the problem is resolved.