CSV is a comma separated value file extension. The data is saved in a single line with commas between values. Those files are usually accessed through spreadsheet software such as Excel. This file format is most often used for values that can be set into a table like an address book, with different values set in lines under different columns(name, email, address, etc.) Because CSV files don't contain any format information they are space contuse and are used for larger database exports and imports.