From Adobe Systems:
Graphic designers, Webmasters, and photographers can create original artwork, correct color, retouch and composite scanned images, and prepare professional-quality separations and electronic output with more flexibility. It features multiple levels of undo and redo, editable text with character-level formatting, flexible and precise color management controls, and built-in support for spot-color channels. Create the highest quality images more efficiently than ever before with this powerful upgrade from Photoshop 7.0.
"CS" is the new version denominator for Adobe's professional design and layout tools. For example, Photoshop CS is the new, full-upgrade version of Photoshop (instead of Photoshop 8.0). Photoshop CS offers an improved file browser for sorting and browsing images, enhanced Match Color command, a Histogram palette, Shadow/Highlight correction tools, and much more.