The comma-separated values (CSV) pseudo-file format is a set of file formats used to store tabular data in which numbers and text are stored in plain-text form that can be easily written and read in a text editor.
In fact, because the goal of reading and writing the format take precedence over consistency, there effectively is no “CSV standard”: only the understanding that plain text is delimited by a symbol.
The CSV file format is very simple and supported by almost all spreadsheets and database management systems. Many programming languages have libraries available that support CSV files. Many implementations support changing the field-separator character and some quoting conventions, although it is safest to use the simplest conventions, to maximize the recipients' chances of handling the data.
Microsoft Excel will open .csv files, but depending on the system's regional settings, it may expect a semicolon as a separator instead of a comma, since in some languages the comma is used as the decimal separator. Also, many regional versions of Excel will not be able to deal with Unicode in CSV. One simple solution when encountering such difficulties is to change the filename extension from .csv to .txt; then opening the file from an already running Excel with the "Open" command.
Detailed info : http://en.wikipedia.org/wiki/Comma-separated_values