Vector graphics

Vector graphics (also called "object-oriented" graphics, though unrelated to object-oriented programming) is used to display separate shapes, such as lines, polygons, text, and groups of such items, as procedurally defined objects, in contrast to bitmaps or raster graphics, which are defined on a pixel-by-pixel basis.

Description
The advantage of vector graphics ("drawing") programs over bitmap ("pixel") editors is that multiple overlapping elements can be manipulated independently without needing to use different layers for each one. It is also easier to render an object at different sizes and to mathematically transform it in various ways without having to worry about and pixelation.