From Wikipedia:
Cross-stitch is a form of sewing and a popular form of counted-thread embroidery in which X-shaped stitches in a tiled, raster-like pattern are used to form a picture. Cross-stitch is often executed on easily countable fabric called Aida cloth, whose weave creates a plainly visible grid of squares with holes for the needle at each corner. Counted cross-stitch projects are worked from a gridded pattern called a chart and can be used on any count fabric; the count of the fabric and the number of threads per stitch determine the size of the finished stitching.
Counted cross stitch could be defined as the art of painting with embroidery floss on fabric. By following a chart and stitching X's on a piece of evenweave fabric, a beautiful picture is easily and quickly created.