Obfuscation :
A way in which spammers hide their spam messages so the will not be detected, can also be used to describe Munging.
OEM
Software :
Stands for Original Equipment Manufacturer software. This software comes pre-installed on new or refurbished Hardware, and can not be transferred to another computer.
Open Relay :
An SMTP email server that can allow third party relay of email messages. Spammers may hijack these servers and use them to send spam.
Operating System :
This is the interface a person sees when using a computer, and makes the whole system user-friendly by providing a desktop, taskbar and shortcut icons. Operating Systems include Windows and Mac OS.