Shapefiles are the dominant file format used for spatial data (of the "vector" type: points, lines, polygons). All GIS programs can import them, and many, like DIVA-GIS, use them directly. A shapefile consists of multiple files: .shp, .shx, .dbf, and sometimes more. The attributes (data records) of the spatial features are stored in the .dbf file. That was convenient because these files could be easily edited with Microsoft Excel -- which is installed on the vast majority of windows computers. Unfortunately, in recent versions of excel (Office 2007) you can only open a .dbf file, but you can not save it. That is a real hassle for shapefile users.
DIVA does not have dbf editing. And it is a pain in programs that do (ArcMap); most people prefer the excel backdoor. Now what?