The WIP tag allows you to specify things that are a work in progress. One common situation where this might be useful is if you have a person or item that you want to write about, but you haven't quite yet found a good name for them. In such a case, you could use the <wip></wip> tag to signify that the thing's name is temporary. Here's an example:
The trombone is a musical instrument in the brass family. As with all brass instruments, sound is produced when the player's vibrating lips (embouchure) cause the air column inside the instrument to vibrate. Unlike most other brass instruments, which have valves that, when pressed, alter the pitch of the instrument, trombones instead have a telescoping slide mechanism that varies the length of the instrument to change the pitch. However, many modern trombone models also have a valve attachment which lowers the pitch of the instrument. Variants such as the valve trombone and superbone have three valves similar to those on the trumpet.
You can even make whole sentences wip.
Sattler had a great influence on trombone design. He introduced a significant widening of the bore (the most important since the Renaissance), the innovations of Schlangenverzierungen (snake decorations), the bell garland, and the wide bell flare—features still found on German-made trombones that were widely copied during the 19th century.