It used to mean "advance the terminal to the end of the paper sheet" or "advance the terminal by a sufficient number of lines that the current line of text is above the edge you use to tear the paper off", back when computer terminals were basically typewriters.(This description assumes that you're old enough to know what a "typewriter" is.)
For plain terminals, it was also used to clear the screen.
Basically it means "insert page break", and I believe that some word processing apps are smart enough to turn the form feed character into a page break in printer-rendered output.
You probably don't need to worry about it.