to mark something with small specks or dots, either with a medium such as paint or ink or by engraving its surface;
e.g. She used a fine brush to stipple the painting with flecks of paint.
(verb)
to use small, repeated touches to do something such as apply paint or roughen a material's surface;
e.g. He used a sponge to stipple the wet paint to give it a special effect.
(noun)
an artistic technique in which small dots are used to give the impression of light and shade/dark, the process of using such a technique, or the output/effect of the technique;
e.g. I decided to use a stipple to show the shadow of the object in my drawing.