A segment is the piece of your journey you can accomplish with one flight coupon. During the "segment" your airplane may stop one or more times. You may even get off and board a different aircraft (although it will continue on using the same flight number). As long as the one coupon got you on that entire journey, it's one segment.

A stopover happens when you stay in a city for 24 hours or longer, or when you make your way from the city in which you arrived on an OWE flight, to a different city from which you'll continue your OWE journey. Stopovers aren't counted except in your continent of origin, where you're only allowed two. In your continent of origin, after those two stopovers (which can be almost a year long, if you care), when you end one segment you must begin the next in less than 24 hours (unless there's simply no flight that soon. Note that "with available seats" isn't in the sentence.)

You cannot bounce all over the place because although stops aren't limited except in country of origin, segments are. As you noted, you get six in North America (which includes Central America).