MINTEMP triggered
Your printer measured a temperature below its configured minimum on hotend, bed and/or chamber.
Make sure to keep your printer in an environment that isn't colder than its configured minimum temperature (15°C is quite common here). Also check your printer's thermistors and make sure they still measure correctly.
Consult your printer's or printer firmware's FAQ or community if you need help with that.
MAXTEMP triggered
Your printer measured a temperature above its configured maximum on hotend, bed and/or chamber.
Make sure you don't try to heat up your printer beyond its specification. Also check your printer's thermistors and make sure they still measure correctly.
Consult your printer's or printer firmware's FAQ or community if you need help with that.
Thermal runaway
Your printer found a mismatch between its heating output and the measured temperatures on hotend, bed and/or chamber. Detection of this is a safety feature that catches cases of heater cartridges or thermistors fallen out of heating blocks or off a print bed.
You need to do a full check of your printer's wiring, thermistors and heaters.
Consult your printer's or printer firmware's FAQ or community if you need help with that.
Heating failed
Your printer was not able to heat up hotend, bed and/or chamber to the desired target temperature. Detection of this is a safety feature that catches cases of heater cartridges or thermistors fallen out of heating blocks or off a print bed.
This can also happen if you forget to simply power on your printer (on some printer models the serial connection to OctoPrint can and will work just fine without the printer being actually powered up thanks to backpowering), so make sure it is actually turned on properly.
If it isn't that simple of a solution, it could also be a case of a wrong PID tuning, a failing heater or a broken connection, or a broken thermistor. You need to do a full check of your printer's wiring, thermistors and heaters and also might want to run a PID tuning.
Consult your printer's or printer firmware's FAQ or community if you need help with that.
Probing failed
Probing your bed for automatic bed leveling failed. This can have several reasons, ranging from your leveling probe not being able to activate or being broken, your bed being so far out of tram that it can not be leveled through software alone, a probe point being unrecoverable or more.
As a solution for this heavily depends on your specific bed leveling setup, we recommend you check your printer's FAQ or community.