“GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring.”
This is a great piece of image editing software that I’ve been using for years and has become a vital piece of my software armoury. With a feature set not unlike Adobe Photoshop (although Photoshop is more able in some respects), GIMP has the major advantage of being Open Source.
This not only means that it’s entirely free (and will always be) but that it also receives regular updates to provide new features and tweaks.