Convert topojson to osm

What is the difference between .topojson and .osm?

Description: TopoJSON is a file format for encoding geographic data structures, based on the GeoJSON format. It encodes geometries more efficiently and supports topology, which enables more accurate representations of geographic objects. TopoJSON eliminates redundancy and simplifies data, making it smaller and easier to work with.; An OSM file contains street map information in the OpenStreetMap (OSM) format. It saves XML-formatted data in the form of "nodes" (points), "ways" (connections), and "relations" (street and object properties, such as tags).