There's always been a certain degree of confusion as to the definition of "orphans", "widows" and "runts" in typography. Runts are occasionally referred to as orphans, which does not help matters. And they are sometimes (mistakenly) called widows, too. So let's just clear this up once and for all:
InDesign has a few features to help deal with runts. The first of these is in the hyphenation control. You can disable the hyphenation of the last word in a paragraph in that paragraph's style options (and set various other limits, too). So far, so good.
To deal with runts that are whole words, we need to bring out the big guns: GREP styles. It's worth getting to grips with GREPs if you manipulate text a lot, as they can save a lot of time in typesetting. Here's how I do things:
That's all there is to it. If you want to change the length of what's considered a "runt" (to make it shorter, for example), just change the 5 to 3 or 4.
Unfortunately, InDesign has precious few to deal with orphans and widows, which I check for manually. This is a bit tedious and I've developed some scripts to locate them, but really it all depends on the dynamics of the text on the page, so it needs a bit of human love.