An illustration is a displayed visualization form presented as a drawing, painting, photograph or other work of art that is created to elucidate or dictate sensual information (such as a story, poem or newspaper article) by providing a visual representation graphically. wikipedia.org

Concept art is a form of illustration where the main goal is to convey a visual representation of a design, idea, and/or mood for use in films, video games, animation, or comic books before it is put into the final product. wikipedia.org

Adobe Illustrator is a vector graphics editor developed and marketed by Adobe Systems. wikipedia.org

Drawing is a form of visual art that makes use of any number of drawing instruments to mark a two-dimensional medium. Instruments used include graphite pencils, pen and ink, inked brushes, wax color pencils, crayons, charcoal, chalk, pastels, various kinds of erasers, markers, styluses, and various metals. wikipedia.org

Digital painting is an emerging art form in which traditional painting techniques such as watercolor, oils, impasto, etc. are applied using digital tools by means of a computer, a digitizing tablet and stylus, and software. wikipedia.org

A sketch is a rapidly executed freehand drawing that is not usually intended as a finished work. A sketch may serve a number of purposes: it can be used to record something that the artist sees, develop an idea for later use or as a quick way of graphically demonstrating an image, idea or principal. wikipedia.org