To clean data is to run an existing database against a more accurate, complete database in order to correct for corrupt, inaccurate, or outdated data. Data cleansing, in practice, is often used by companies who collect data on their customers. Customer information such as business name, contact name, address, phone number etc. are recorded by the company, but by the end of the year, much of this data is inaccurate or out of date, whether due to businesses changing locations, changing employees, companies closing, etc. Data cleaning is a byproduct of the data append process, which allows for the addition of other vital data elements  such as NAICS Codes, Company Size Information and more.