A follow-on is something done or made after something else, to continue it or as the next step: a follow-on book, a follow-on product, a follow-on study. Companies talk about a follow-on to a successful phone; teachers set a follow-on activity. It comes from the phrasal verb follow on. In cricket, a follow-on is a special rule that sends one team in to bat again — a sports use of the same “you have to go on” idea. Fairly neutral; a bit office-and-news in the “next product” sense. Though actually, many people just say follow-up, which is close: follow-up often means checking later, while follow-on often means the next thing in a series.