It means you should make sure you have working smoke detectors as well as a fire extinguisher; then call an electrician!
You didn't say if an applicance was plugged into the outlet at the time. If so, you need to unplug the applicance and determine why the outlet is hot. If this applicance is high wattage, then probably all that is needed is to replace the outlet. If no applicance is plugged into the outlet you likely have a applicance plugged into the same circuit and it is drawing its needed power through the outlet that is hot. (the outlets are daisy-chained) There are likely loose or corroded connections at this outlet. The outlet needs to be removed (with the power off) and inspected to determined what the problem is that's making it hot. Usually a replacement is all that is needed.
You should turn off the power and replace the outlet regardless . There may well be internal problems that you cannot see.
all three answers are right! it is an easy fix in most cases, if it is hot and there is nothing plugged into it there is something downstream on the same circuit and they have used the outlet as a junction. (you will find both terminals on each side being used) to change the plug make sure the power is off, when i'm alone i use a radio plugged into the socket and switch breakers off and on until i don't hear it! make sure the wires are tight on the new plug, gold screws get black wires, silver screws get white, and the green screw gets the green or bare wire. if there wasn't plugged into this outlet when you found it hot while the power is off take the radio around to the other outlets and see what others are on that circuit and you might find the outlet with high wattage. this could be an appliance or space heater, anything that has a heating element or motor.
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Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them