In ETL, the transformation is happening after the data has been extracted from the source system but before it is loaded into the target system and within the data pipeline platform itself, typically by relying on an in-memory engine to aggregate, join and manipulate data.
In an ELT pipeline, the data is loaded into the target system – typically a powerful modern database – and then transformed with the database’s compute power. Data pipeline tools can be used to ensure schema consistency and to allow developers to manage the flow of data with minimal coding.