Part of macOS
fontdFonts
○ Leave it
Manages the fonts installed on your Mac.
What it is
Serves fonts to apps.
If you stop it
macOS starts it again straight away. Leave it.
The verdict
○ Leave it. Part of macOS, or something that starts again by itself. You never need to close these.
In Activity Monitor
fontdfontworker
From Procession’s guide, in the words the app shows.