Data Integration, also known as ETL (Extract, Transform, Load), means combining data from different, often heterogeneous, sources in a way that provides a unified view on this data. It is typically used for integration of different applications and is therefore essential in an enterprise environment. Another term that is ofted used in conjunction with data integration is Data Warehouse, a report-friendly data store.
As a database specialist, I've been involved in data integration tasks throughout my entire career. I'm a certified Informatica PowerCenter developer (PowerCenter is one of the most powerful ETL solutions on the market). I have also developed a lightweight ETL application in Python myself.