Data integration involves combining data from different sources while providing users a unified view of the combined data. This lets you query and manipulate all of your data from a single interface and derive analytics and statistics. You can also visualize and even migrate your combined data to another data store for longer-term storage and further analysis.
ETL for extract, transform, load and includes a process by which heterogeneous data is made homogeneous. The transform step typically adjusts data schema and format to work with the target data warehouse, prior to loading it. During this final load step, data is written to the target database or data warehouse.