{{no indent}}—and its short alias {{ni}}—is a convenience wrapper around {{text-indent|0|…}}. All it does is call the underlying template with the length parameter set to zero. It is intended for text which should never be indented, even on user agents (like ebook readers) that indent the first line of a paragraph by default. This may be needed for things like the salutation of a letter, or the text following an image when the image breaks up a paragraph.
Usage edit
Example
{{ni|This text is flush left on all user agents.}}
This text is flush left on all user agents.