A comma-separated value (CSV) file is a flat data file in which variables are separated by commas. Typically, CSV files have a file extension of .CSV. This file format is useful when their variables cannot contain commas and when there is limited metadata.
CSV files are similar to comma-delimited files, except there are some additional rules. For example, where a variable contains commas, it is surrounded by quotes. For example:
Age,Gender,Reason for defection
3,2,Forgot to pay
1,2,"I hate you because you are too expensive, difficult to deal with, and suck!."
This file format is poor if there is substantial metadata
As with all flat data files, this format is poor when there are substantial amounts of metadata. For example, it is typically a poor file format for survey data. See Flat Data Files for more information about problems with the use of this file format when there are substantial metadata.