Abbreviations in vi editor are the shortcuts for strings. For example, if you frequently need to write the text "Change review not needed", you can have a shortcut like "crn" for this. So every-time you require to type "Change review not needed", you type crn (then a space) and your abbreviation will be expanded (in insert mode).
With my vi editor version:
VIM - Vi IMproved 7.1 (2007 May 12, compiled Jan 8 2009 02:24:14)
I created an abbreviation on my .vimrc:
$ tail -4 ~/.vimrc
:ab crn Change review not needed
This abbreviation ("crn") was not working as expected and later I came to know its because of the "set paste" option set on my .vimrc. Vi abbreviations are disabled if the 'paste' option is on. I removed the ":se paste" from my .vimrc and the above abbreviation worked.
Another alternative to set an abbreviation in vim
:inoremap crn Change review not needed
This also require the 'paste' option to be unset/not set.
To unset an abbreviation in vi editor, type in ex mode:
To see what all abbreviations are already set, type in ex mode:
For help on vi abbreviation type, type in ex mode: