Extract, Transform & Load is a process in Data Warehousing. ETL refers to, "Extraction of data from different applications" developed & supported by different vendors, managed & operated by different persons hosted on different technologies "into Staging tables-Transform data from staging tables by applying a series of rules or functions - which may include Joining and Reduplication of data, filter and sort the data using specific attributes, Transposing data, make business calculations etc - to derive the data for loading into the destination system-Loading the data into the destination system, usually the data warehouse, which could further be used for business intelligence & reporting purposes.