Ways to store data in files. Text: CSV (delimited), JSON, and XML (semi-structured). Binary: Parquet and ORC (columnar, ideal for analytics) and Avro (row-based, with the schema in a JSON header).
In DP-900 you are asked to pick the format: columnar and compressed for queries that read few columns → Parquet; row-based binary with an embedded schema for messaging → Avro; format created for Apache Hive → ORC.
Data file formats is a concept that can show up on the exam. Check the full guide to see it in context.