Raster = Pixel Maps, Vector = Content Described by Code
There are two main approaches to storing images on a computer: using bitmaps (Raster Images, aka Bitmaps) and using mathematical formulas to describe them (Vector Images).
Bitmaps (Raster)
A pure bitmap (not compressed into any sort of compression format, like “jpeg” or “gif”) would describe a grid of pixels, each of which with a certain number of bits reserved to describe their color content (typically an even number of bytes, 8 bit, 16 bit, and so on). A pure bitmap could say that the top-left pixel is pure red. So, pixel in position 0,0 has an RGB value of (255, 0, 0).
Vectors
Vector images are stored as lines of code. This is fundamentally different from the bitmap approach. A simple ”SVG” file, when opened in a text-editor, can be pretty easily parsed by a human with some graph paper. Since mathematical formulas can describe continuous curves, you can infinitely zoom in or out on a Vector image and not lose fidelity.