Focus on Files and Filegroups
April 28, 2009[From SQL Server Magazine]
If you're like most SQL Server DBAs today, you often wonder how many data files or filegroups you should have when you create a new user database. If you're not sure about the difference between a file and filegroup and the purpose of each, a data file is an OS file in which SQL Server stores the contents of the database (e.g., data, indexes, metadata) on the physical storage medium, and a file group is a logical container for managing or grouping one or more data files.
The article continues at http://www.sqlmag.com/Articles/Index.cfm?ArticleID=101621