Pixel art is a form of digital art wherein images are created and edited at the pixel level using a graphics editing software.
What defines pixel art is its unique visual style, where individual pixels serve as the building blocks that make up the image.
The effect is a visual style very similar to that of mosaic art, cross-stitch and other types of embroidery techniques.

Dithering is a shading technique where you apply a pattern to a color band to make
transistions smoother.

(Source : Techopedia)