Her's another letter game.

Name a photoshop tool, filter or whatever photoshop related thing starting with the first letter of the previous one. If there's none to be found (or the answer is taking to long), you can also name a closely related one.

If possible, please indicate what this tool can be use for (with or without images)

I start with:

Gaussian Blur

applying a Gaussian blur to an image is the same as convolving the image with a Gaussian or normal distribution. Each pixel's value is set to a weighted average of that pixel's neighborhood. The original pixel's value receives the heaviest weight (having the highest Gaussian value), and neighboring pixels receive smaller weights as their distance to the original pixel increases. This results in a blur that preserves boundaries and edges better than other, more uniform blurring filters; see also scale-space implementation.

Typically it's used to remove noise or reduce details (mimicing out of focus, smoother skin,... etc)focus objects.

Great Grefix, I will sit back and wait what happens next. You can complement your entry with a link to a good tutorial, about the same tool, filter, that way this forum could become a gate to the best tutorials that are now hidden in other forums or on other pages.

Brush Tool
here's a link
http://akvis.com/en/photoshop-tips/brush-size.php

Turbulence Tool (in liquify)

here's a fairly basic liquify tutorial http://www.peachpit.com/articles/article.aspx?p=30690&rl=1