What is CSV?

The csv format (comma separated values) is defined in RFC 4180.

The data format is a simple line based text format to exchange tabular data between multiple applications like Excel.

Each line is build of fields, each separated by a delimiter. The default for this delimiter is a comma as supposed by the name of the format but others like semicolon are also common. If the delimiter appears in the field value, the whole value is quoted. Any quote in the field value will by doubled.