What is ETL and ELT
ETL is a data integration pattern that emerged in the 1970s where you Extract data from multiple applications and other sources, Transform it, and then Load it into different targets. It is most commonly used for loading data into data warehouses. But it is also widely used for data migration (from one application or database to another), for loading data marts, for operational data synchronization and master data management; even application integration.
ETL became associated with data integration vendors such as Informatica. But there were other variants, such as ELT. For example, people would use Informatica to Extract and Load data into Teradata, where they would then Transform data using TQL (Teradata Query Language.) ELT became popular with data lakes where you would load raw data and transform it later when needed. It helped shorten the time it took to create new reports. People may see ELT as the newer approach, and ETL as older. But in reality many companies do ETLTLTLTL across their data pipelines.
There is also some TEL in blockchains. But for the most part the software industry has limited the variations to ETL and ELT. Hopefully it will not LET other variations happen ...