What Excel is
An Excel workbook is a zip archive of XML parts describing sheets, cells, formulas, styles and charts. The .xlsx extension is that format; .xls is the older binary one from before 2007.
Finance, operations and anyone who received a file from finance or operations.
What Ruby is
A Ruby array of hashes with symbol keys.
Rails seed files and Ruby scripts.
What changes when you convert Excel to Ruby
Only the first sheet is read, and cells are read as the text Excel displays rather than the number underneath. That matters for dates: a cell showing 15/03/2026 arrives as that string, not as a serial number you would then have to decode.
Column names are converted to valid symbol names, which means non-word characters become underscores.
What carries over from Excel to Ruby
Excel records 2 things about a table that Ruby has no way to hold.
Ruby has no header row. The column names are repeated as keys on every record instead, which is why the result is bigger on disk than the table it came from.
Anything visual in the Excel - weight, alignment, colour, column widths - has no counterpart in Ruby and is dropped. The values are what survives.
Both formats record types, so numbers, booleans and nulls survive as themselves rather than as text.