Dedupe is a synonym for data deduplication or de-duplicate. Dedupe is the process of eliminating duplicate entries from a data set.
The term is used both in computing and for non-technical people.
In computing, deduping is performed in software development to remove duplicates in a list. Still with computing, data deduplication is used with files too. In a system that store files, deduplication is a technique to list all similar files and their reference in documents, emails, etc., and to remove all redundant files to keep only one version and have all references point to those single files.
Dedupe is also used for non-technical people to define the action of finding and merging redundant duplicates. A good example is CRM deduplication. CRM applications store contact information for leads, customers, etc. Several CRM records can represent the same person or business and hold different and complementary data. In this example, merging duplicates in the CRM is important to build a single view for every user. It also lower software cost as it reduces the number of items to store in a database.