This file is used by synonym filter to replace the tokens with their synonyms. For example, a search for "DVD" may expand to "DVD", "DVDs", "Digital Versatile Disk" depending on your mapping in this file. The following is how you can specify the synonyms:
GB, gib, gigabyte, gigabytes
MB, mib, megabyte, megabytes
Television, Televisions, TV, TVs
Incident_error, error
In this file, you can also make spelling corrections, for example, assasination can be changed to assassination.