GDM - Gnome Display Manager. Used to describe the software package as a whole.
gdm - The Gnome Display Manager daemon (gdm).
Greeter - The graphical login window (gdmlogin).
Chooser - The host chooser which appears on remote displays sending INDIRECT queries (gdmchooser).
Paths without a leading '/' are relative to the installation prefix. I.e. share/pixmaps/ refers to /usr/share/pixmaps if GDM was configured with --prefix=/usr.