Quantum GIS is open source software available under the terms of the GNU General Public License meaning that its source code can be downloaded through tarballs or the git repository. This is written in c++ and has some libraries in Qt.
QGIS is GIS application with which you can you can mange, edit, or visualize your map. Infact this is wonderful tool with which you can make your map beautiful.
Now,as we know that our OSM data consist of Nodes, Ways and Relations. Here I must not forget to mention again “OpenStreetMap is a web-based map to which any registered user can submit data.”
Node is a a latitude/longitude pair of coordinates. A way is a list of at least two nodes describing a linear feature like street, or something similar. And third one Relation is used to specify relationships between objects. This relation isn’t much clear to me but one can look here for more information.
And in Quantum GIS, these are displayed as three separate layers: Point layer, Line layer and Polygon layer.
All three layers are equally important.
The data that lives on the OpenStreetMap can be downloaded and used inside of a QGIS for geospatial analysis, rendering, and for other geo-related tasks.
Now,what is thing that makes connection between our Standout, dignitary OSM data and Quantum GIS ?
The QGIS OpenStreetMap Plugin, plugin for QGIS, adds support for OpenStreetMap raw vector data, bring it in as a layer either from .osm XML file or by direct download from the OpenStreetMap API. With it you can even edit or upload back to OSM data.