Think of it as housecleaning for your data. ETL stands for extract, transform, and load. ETL is software that enables businesses to consolidate their disparate data while moving it from place to place, and it doesn't really matter that that data is in different forms or formats. The data can come from any source. ETL is powerful enough to handle such data disparities.
For example, a financial institution might have information on a customer in several departments and each department might have that customer's information listed in a different way. The membership department might list the customer by name, whereas the accounting department might list the customer by number. ETL can bundle all this data and consolidate it into a uniform presentation, such as for storing in a database or data warehouse.
Another way that companies use ETL is to move information to another application permanently. For instance, word-processing data might be translated into numbers and letters, which are easier to track in a spreadsheet or database program. This is particularly useful in backing up information as companies transition to new software altogether.
One important function of ETL is "cleansing" data. The ETL consolidation protocols also include the elimination of duplicate or fragmentary data, so that what passes from the E portion of the process to the L portion is easier to assimilate and/or store. Such cleansing operations can also include eliminating certain kinds of data from the process. If you don't want to include certain information, you can customize your ETL to eliminate that kind of information from your transformation.
The T portion of the equation, of course, is the most powerful. ETL can transform not only data from different departments but also data from different sources altogether. For example, data in an email program such as Microsoft Outlook could be transformed right along with data from an SAP manufacturing application, with the result being data of a common thread in the end. Microsoft, of course, makes an ETL package, as do Oracle and IBM.