What is KMZ?

A zipped KML, sometimes with icons and images bundled alongside. It's what Google Earth hands you when you export, and it's a single attachment rather than a folder, which is most of the appeal.

What is GeoJSON?

The format web maps speak - points, lines and polygons as plain JSON, with arbitrary properties hung off each feature. Leaflet, Mapbox and every mapping library read it natively, which makes it the usual destination for map data that came from somewhere else.