Vector graphic

A vector graphic describes an image as shapes, lines, curves, and fills defined by math, rather than as a grid of pixels. Because it is math, a vector can scale to any size and stay perfectly sharp: a logo drawn as vectors looks crisp on a business card and on a billboard.

Inside a PDF, things like logos, icons, charts, diagrams, and the outlines of text are typically vector. That is why you can zoom way into a well-made PDF and the lines stay clean instead of turning into blocky pixels. Vectors also tend to be compact, since a shape is cheaper to store than every pixel that makes it up.

The trade-off is that vectors suit graphics with defined edges, not photographs. A photo has too much subtle detail to describe as shapes, which is where raster images come in. Most real PDFs mix both: vector logos and text alongside raster photos.