About [[Osm:Browse.in changeset/de]]
Short: a set of changes to existing objects or new objects to add to the OSM database
Long:
An OSM user performs changes to OSM data using software like JOSM and iD who utilises the OSM API to create and communicate to the OSM servers the wanted changes in blocks called changesets. Changesets associates otherwise unrelated changes to objects into a logical group with common metadata (user, date, changelog, software used, etc.) to avoid storing this data redundantly for each object and to ease administration (fx. a changeset can be reverted if it is determined that it contains unwanted edits).
Each changeset is given a unique reference number by the API, fx. my latest changeset is #83475681.
Long and technical: see OSM wiki