Data loading, or simply loading, is a part of data processing where data is moved between two systems so that it ends up in a staging area on the target system.
With the traditional extract, transform and load (ETL) method, the load job is the last step, and the data that is loaded has already been transformed. With the alternative method extract, load and transform (ELT), the loading job is the middle step, and the transformed data is loaded in its original format for data transformation in the target system.
Traditionally, loading jobs on large systems have taken a long time, and have typically been run at night outside a company's opening hours.