In graphics and image-editing programs the painting tool
changes the area of your image where you use the cursor
to add paint strokes to the image. You can use this tool to do tasks such as fill in single pixels, add hard or soft lines, or select areas to fill with a solid color. Some programs will allow you to paint with a texture rather than a single color.
See also “Graphics Software Terminology” in the Quick Reference section of Webopedia.