Vector
Artwork defined by mathematical paths rather than pixels, so it scales to any size without losing sharpness — the opposite of a raster (pixel-based) image.
Also called: vector graphic, raster vs vector
Vector graphics (AI, EPS, SVG, PDF) store shapes as points, curves and fills, so they stay crisp at any size — which is why a logo should always be supplied as vector. Raster images (PSD, JPG, PNG) store a fixed grid of pixels and blur or pixelate when enlarged past their resolution.
A mockup is usually a raster scene (a photograph) into which you place vector or raster artwork via a smart object; keeping the placed logo as vector preserves its edges at large display sizes.