http://www.purl.org/tcl/home/man/tcl8.4/TkCmd/grid.htm
Grid is one of several Geometry Managers. Some others are pack and place.
For a simple example, see A little spreadsheet.
DKF - The term Grid also refers to the very high end of resource sharing systems over the internet which it is likely that people will be hearing a lot more about in the future, especially in phrases like Grid Services...
Tk syntax help - Arts and crafts of Tcl-Tk programming - Category Command