Vector-based digital image is a mathematical equation, which incorporates the dots line to become an object, so the image is not to be broken even if enlarged or reduced (unlike bitmap images). That's why Vector is widely used to design the logo. Another version states, in computer graphics, a line is signified by the end point (XY or XYZ coordinates). When a circle is drawn, the circle is made up of many small vectors.
Vector images are generally smaller when compared with a bitmap image. Some vector image formats such as SVG, EPS, CDR, AI, SWF, etc..