Apache Parquet is a free and open-source column-oriented data storage format in the Apache Hadoop ecosystem. It's specifically designed for efficient and performant flat columnar storage format of data compared to row-based files like CSV. When it comes to data processing, Parquet lowers storage costs while increasing performance. It provides features such as data compression and encoding schemes, that are more efficient to process. Its schema evolution ability lets users start with a schema, evolve it over time, and still be able to read the older data. This flexibility in reading data from older schemas is an added advantage for users. Due to these unique capabilities, it's a favorite among data engineers and scientists working in the data analysis field.