A comma-separated values (CSV) file is a delimited text file that uses a comma to separate values. Each line of the file is a data record. Each record consists of one or more fields, separated by commas. The use of the comma as a field separator is the source of the name for this file format. A CSV file typically stores tabular data (numbers and text) in plain text, in which case each line will have the same number of fields.

The CSV file format is not fully standardized. Separating fields with commas is the foundation, but commas in the data or embedded line breaks have to be handled specially. Some implementations disallow such content while others surround the field with quotation marks, which yet again creates the need for escaping if quotation marks are present in the data.

The term "CSV" also denotes several closely-related delimiter-separated formats that use other field delimiters such as semicolons. These include tab-separated values and space-separated values. A delimiter guaranteed not to be part of the data greatly simplifies parsing.

Alternative delimiter-separated files are often given a ".csv" extension despite the use of a non-comma field separator. This loose terminology can cause problems in data exchange. Many applications that accept CSV files have options to select the delimiter character and the quotation character. Semicolons are often used instead of commas in many European locales in order to use the comma as the decimal separator and, possibly, the period as a decimal grouping character.