CSV (Comma Separated Values) files are the most common format for storing tabular data. Values in a row are separated by commas and rows are separated by newlines.

CSV files often start with a header row that has column names, but this is not required.

Each row in a CSV file must have the same number of values as the header row.

CSV files do no enforce types or a schema. This means that each column can have multiple types, which can make analysis difficult and compression inefficient.

Parquet files can be easier to analyze and compress better than CSV files.

Apache Parquet (.parquet) is a format that was designed for storing tabular data on disk. It was designed based on the format used in Google's Dremel paper (Dremel later became Big Query).

Parquet files store data in a binary format, which means that they can be efficiently read by computers but are difficult for people to read.

Parquet files have a schema, so means that every value in a column must have the same type. The schema makes Parquet files easier to analyse than CSV files and also helps them to have better compression so they are smaller on disk.