The basic function of Adobe Illustrator is to create and edit vector images (graphics).
The term "vector graphics" is mainly used today in the context of two-dimensional computer graphics. It is one of several modes an artist can use to create an image on a raster display. Other modes include text, multimedia, and 3D rendering. Virtually all modern 3D rendering is done using extensions of 2D vector graphics techniques.
Vector graphics editors typically allow rotation, movement (without rotation), mirroring, stretching, skewing, affine transformations, changing of z-order (loosely, what image is in front of what other image) and combination of primitives into more complex objects.
More sophisticated transformations include set operations on closed shapes (union, difference, intersection, etc.).
Vector graphics are ideal for simple or composite drawings that need to be device-independent, or do not need to achieve photo-realism. (Designing clip art for example.)