All STOP codes are displayed in hexadecimal format, preceded by a 0x. For example, a popular STOP code seen on a Blue Screen of Death is STOP 0x0000008E.
STOP codes can also be written in a shorthand notation with all the zeros after the x removed. For example, the abbreviated way of representing STOP 0x0000008E would be STOP 0x8E.
The STOP code is displayed on the blue screen after the system crash and can be used to troubleshoot the specific issue that caused your problem.
More information on individual STOP codes can be found on my Complete List of STOP Errors.
Some STOP codes share code numbers with some of these other types of error codes but they are completely different errors with different messages and meanings.