What is JSON?
JSON is the shape data arrives in when it comes from an API. Tabular data usually lands as an array of objects, one per row, with the column names repeated as keys in every single one - verbose to read, but unambiguous.
What is CSV?
CSV is the least glamorous and most durable data format there is - rows of values separated by commas, readable by every spreadsheet and database ever written. Its subtleties are all about quoting: a value containing a comma has to be wrapped, and a quote inside that has to be doubled.