Arrays do not have "columns". :-)
You can have two kinds of rank-2 arrays in .NET — rectangular and jagged. The rectangular array has fixed dimension. It's more like a regular rank-1 array interpreted (indexed) as rank-2 array, using the knowledge of the dimensions. The jagged array is simply an array of arrays; so each "inner" array can have its individual length.
See this article to get how it looks and works in VB.NET code:
http://visualbasic.about.com/od/quicktips/qt/initjaga.htm[
^].
—SA