It is confusing for me to get the meaning of the symbol when I run the below command:
pm2 status
It shows a table. The confusing part is the square symbol which I have marked in the below picture
What does it actually mean? Are three instances of index server running or something like that?
Quoting @Flimzy comment:
That looks like the Unicode replacement symbol, indicating your terminal cannot display the proper character there.This doc shows an arrow in a similar looking column.
This column/value refer to the process's number of restarts which have occurred since the first run.
To see it in actions, the following command does restart the process pm2 restart <process-name|id>, which will increase the restarts counter by 1.