Illustrator is a vector graphics program developed by Adobe and used by designers to create logos, illustrations, and artwork. It allows you to create scalable graphics that can be scaled up or down in size without losing quality. Illustrator also allows you to create complex shapes and artwork using a variety of tools, including pen and brush tools, shape tools, and more. Illustrator is often used in conjunction with other programs such as Adobe Photoshop to create a complete design package.