CSV stands for Comma-Separated Values, and it's a pretty barebones, plain-text file format that stores tabular data. This means data that'd normally end up in tables or spreadsheets, but in a CSV ...

As long as two programs can both open a CSV file, they can exchange data. For example, ... Open a text editor like Windows Notepad or TextEdit. 2. Click File and then ... Set the File Format to CSV.

Taking this into account, if you’ve mistakenly changed csv to css, Windows may use Notepad to read the file. When you try to open an Excel file, make sure the file’s icon matches the file type.