Files with 2018 extension can be most often encountered as various data or backup files created or generated in the year 2018. Can be pretty much anything, most notably tax and accounting data, calendar or backup files related to the year 2018.
2018 file extension - Any data file created in 2018
What is 2018 file? How to open 2018 files?
File type specification:
File extension 2018 might be used for any data file created in year 2018, typically as some kind of backup to distinguish the data from previous years.
Such files are most frequently used by various tax preparation software, but might as well contain calendar, business or just be backup of some sort.