What is Mail Merge information

Mail Merge is a mass mailing facility using e-mail methods or otherwise that takes names, address and related facts about recipients and merges the information into the form of a letter. Mail Merge printing uses two files one is a data file that contains a listing of data items set in some specific order and second is a master file that contains the standard text as well as the data variables which are replaced with specific data items from the data file through the Merge operation.

In MS Word mail merge that feature which is use for grouping news? It means we send letter lots of client in same time. This is use for mail like form, letter, envelops, directory.