Digital drawings and illustrations are both imaginative creations produced by a talented artist with the assistance of drawing software. Both are created to tell a visual story and inspire the viewer, but the two art forms do possess a key difference.
Digital drawings come from the artist's imagination as a mode of self-expression. The creator might use models for visual reference, but the artist is giving form to their own ideas.
Digital illustrations are made to visually express written instructions or story elements. An illustration might be simple figures that visually outline instructions one step at a time, or perhaps it's an elaborate landscape envisioning a scene or a portrait of a character in a novel.