Picom is a lightweight standalone compositor created for the X Window System.
It is a fork of compton, created because compton wasn't being actively maintained;[1] compton is, in turn, a fork of xcompmgr-dana, forked from xcompmgr.
[2][3][4] Picom can be configured using a config file which in most systems is located at $XDG_CONFIG_HOME/picom.conf.
However, picom can also be started with a custom config file using the following options:[2] Picom has multiple configurations in which it can be run, however in most instances, when using it in conjunction with another window manager, the -b flag is used to start it as a background process.
[2][5]