who are these "other" users?

[JVRudnick]

Hey all...
digging thru my first domain items under 7.5.4, and I found this short list of Web Directory Permissions...

Administrators
Plesk IIS User (IUSR_plasters1)
Plesk IIS WP User (IWPD_2(plasters1))
Plesk Domain User (plasters1)
SYSTEM

I recognize them all except the 3rd one -- who or whom is the IWPD_2(plasters1)) item???

Jim