Adobe Illustrator is a professional vector-based design and drawing program. Used as part of a larger design workflow, Illustrator allows for the creation of everything from single design elements to entire compositions. Designers use Illustrator to create posters, symbols, logos, patterns, icons, etc.
Vector vs. Raster
Computer graphics fall into two main categories: vector graphics and raster graphics. Understanding the difference between the two helps you create, edit, and import artwork appropriately.
What are vectors?
Drawing programs such as Adobe Illustrator create vector graphics, which are composed of lines and curves defined by mathematical objects called "vectors." Vectors describe a graphic according to its geometric characteristics. For example, a bicycle tire in a vector graphic is drawn using a mathematical equation for a circle with a certain radius, set at a specific location, and filled with a specific color. You can move, resize, or change the color of the tire without losing graphic quality because the underlying equations will compensate for your actions.
A vector graphic is resolution-independent, that is, it can be scaled to any size and printed on any output device at any resolution without losing its detail or clarity. As a result, vector graphics are the best choice for type (especially small type) and bold graphics that must retain crisp lines when scaled to various sizes.