Apache Parquet is a columnar storage format available to any project in the Hadoop ecosystem, regardless of the choice of data processing framework, data model or programming language.

Concepts

Block (hdfs block): This means a block in hdfs and the meaning is unchanged for describing this file format. The file format is designed to work well on top of hdfs.
File: A hdfs file that must include the metadata for the file. It does not need actually to contain the data.
Row group: A logical horizontal partitioning of the data into rows. There is no physical structure that is guaranteed for a row group. A row group consists of a column chunk for each column in the dataset.
Column chunk: A chunk of the data for a particular column. These live in a particular row group and is guaranteed to be contiguous in the file.
Page: Column chunks are divided up into pages. A page is conceptually an indivisible unit (in terms of compression and encoding). There can be multiple page types which is interleaved in a column chunk.
Hierarchically, a file consists of one or more row groups. A row group contains exactly one column chunk per column. Column chunks contain one or more pages.

Unit of parallelization