Short for application. Also known as a program.

Example: Winamp is an excellent app for playing MP3's.

A "port" involves transporting, or translating a skin or theme from one program or theme to another. Sometimes ports are from one incompatible operating system to another. (Note: Proper etiquette requires the permission of the original author before porting a skin or theme.)

Example: My new theme for LiteStep is a port of a Linux theme.

Any theft of graphics - skins, themes or graphics taken without the original authors permission. Short for "ripped off".
A person who steals graphics is called a "ripper".

Example: That skin is a rip of my Winamp skin!

see Rip

A graphic, or series of graphics, that when applied to a program, changes the appearance of the program. (Usually, a skin also includes a text instruction file, sometimes called an ini file, to explain to the program how to use the graphics, and where to place them.)

Example: Winamp has more skins than just about any app.

A group of skins that together create a coordinated look to two or more programs.
Example: My theme includes skins for Winamp, Quicknotes, and eFX.

The term theme is also used to describe the skin elements of a larger program that controls the complete desktop's look and feel.

Example: My new theme for LiteStep is a port of a Linux theme.

A shell is a replacement for the Windows Explorer interface. The Windows interface consists of the Start button, the System tray, the Task Bar, and the desktop icons. In other words, all those things that make Windows LOOK like Windows. Shells replace some, or all, of those things with replacements designed to change the look and feel of the desktop.

Shells can emulate the look and feel of alternate operating sytems such as the Apple Macintosh, or Linux. It can also be something completely different such as a fantasy of science fiction theme.

Examples of popular Shells include Litestep, Geoshell, and Talisman (in full shell mode).

also see Shell enhancement

A shell enhancement is a program that runs over the top of the Windows Explorer shell and gives it the APPEARANCE of a different operating system or shell. The difference though is that it is not actually a new shell. When the shell enhancement is closed, your desktop returns to normal.

Examples of Shell enhancement programs include Nextstart, Hoverdesk, and DesktopX.
Talisman can also be used as a shell enhancement, but it also has the ability to run as a full blown shell replacement

Moderation is a word you will see used on skin sites. It means that the administrators of that site limit, or censor certain skins or wallpapers uploaded to that site.
Reasons for moderation vary, but usually the focus of moderation involve one or more of the following:

Nudity, or pornography
Copyrighted material ( such as pictures from movies, magazines, or games)
Poor quality (this is usually a judgement made by one or more administrators)