Glossary
RFC 4180
The specification that defines how CSV quoting works.
RFC 4180 is the closest thing CSV has to a standard. It defines the rules that matter in practice: fields containing a comma, a quote or a newline must be wrapped in double quotes, and a literal quote inside a quoted field is written by doubling it.
This is why naive CSV handling breaks. Splitting a line on commas corrupts any row with a quoted comma inside it, and splitting a file on newlines corrupts any row with a quoted newline. Both are common in real exports, particularly in address and description fields.
Plenty of software deviates from the spec, using semicolons as the delimiter in locales where the comma is a decimal separator, or escaping quotes with a backslash. A parser has to be tolerant of those, but the quoting rules above are what "valid CSV" means.