What does "Process finished with exit code 1" mean?

0 and 1 are exit codes.

exit code (0) means an exit without an errors or any issues, can be a compile time error or any dependency issue.

exit code (1) means there was some issue which caused the program to exit. For example if your program is running on port :8080 and that port is currently in used or not closed, then you code ends up with exit code 1

0 and 1 are exit codes, and they are not necessarily python specific, in fact they are very common.

exit code (0) means an exit without errors or issues.

exit code (1) means there was some issue / problem which caused the program to exit.

The effect of each of these codes can vary between operating systems, but with Python should be fairly consistent.