In the paragraph options, we should have an option for how long the last word in a paragraph must be in order to turn down to its own line. Wording could be "minimum of __ characters on last line" And allow us to turn this feature on or off in addition to specifying the number of characters on the last line.
Raphaël Freeman commented
I call it a runt too! But it would be more useful if one could define it based on the length of the first line indent.
Peter Kahrel commented
Note that an orphan is the first line of a paragraph that ends the page (and a widow id the last line of a paragraph at the top of the page). What Matt describes here doesn't have an official name. 'Short end line', and 'short last line' are the official terms, but 'runt' (coined by David Blatner) is gaining in popularity.