Understanding background and foreground processes

Hello,  I'm working with SM 9.34 and I'm trying to understand background and foreground processes. Please if there's documentation about it.

Examples :  looking at System Status (and the schedule table)

linker is a process and "has" a related schedule record with sched.class linker that "runs" a Javascript

report is a process and "has" a related schedule record with application pa.main.appl.bg and some parameters in the Strings folder

Then I supposed linker and report are background processes, that's why they are scheduled to run periodically

SMTPmail is a process  and it hasn't a related schedule record so I supposed it's a foreground process ¿does it means it runs immediatly and is not scheduled?

Thanks in advance,