Application return codes are specific to the application that the task is running. the task moniter stores the last exit code, which is the code the application returns when it exits. When trying to decipher what the return code means for a specific application or patch, the documentation for that application or patch usually contains some relevant information.
The extent to which applicaiton return codes are docuemented varies from application to application and some applications and patches don't offer any explanation describing return codes. Usually an App Code: 0 is success wheras any other return code means failure, but all return codes are application specific.