FLDTYPES.XML defines how the different field types that are used in Web sites based on SharePoint Team Services from Microsoft are rendered. It is located at Program Files\Common Files\Microsoft Shared\web server extensions\50\templates\1033\xml.
If you add a column, you can choose the type of information, or field type, that is used to render the column. Two elements that you will probably be interested in using are the following:
See Example 1 — Adding a new field type for Flash movies for an example about how to edit FLDTYPES.XML to add a new field type to your Web sites based on SharePoint Team Services.