AWS Glue is a fully managed extract, transform, and load (ETL) service that makes it simple and cost-effective to categorize data, clean it, enrich it, and move it reliably between various data stores. AWS Glue can read data from a variety of data sources including Amazon S3, and transform it into a columnar format like Parquet, which is more space-efficient and faster for analytics, without the need to write any conversion code. This is because AWS Glue provides built-in transforms, and also supports an environment for developing custom ETL code when needed.