application/vnd.ms-excel

The binary Excel workbook of 1997-2003: BIFF record streams packed inside an OLE2 compound file. That container's d0 cf 11 e0 signature is identical across binary Word, Excel and PowerPoint — it is listed once, under application/msword — so a sniffer that stops at the magic knows only that it found a compound file, and must locate the Workbook stream to call it Excel. The type is doubly abused in the wild: sent for modern .xlsx files, which have their own long OOXML type, and slapped on CSV downloads as a folk trick to make browsers hand them to Excel.

The registry maps a small museum onto this type — .xlt templates, .xla add-ins, .xlm macro sheets — all the same binary container.

Defined by [MS-XLS] — Excel binary file format (.xls) · IANA registration. Registry facts from the IANA media-types registry via mime-db.