Confusion over anime length

When I see that an anime has 24 episodes, I assume that that is the full series. However, in many cases I have discovered later that there is a second season (normal) or a third season but only 12 episodes. What I mean by that is that season 1 is 24 episodes, season 2 is 24 episodes but season 3 is only 12 episodes. There may or may not be a 4th season after that.<br><br>I find this a bit confusing. I am not sure if there is a Japanese term for this but I don't want to be starting up a new series only to find that it is incomplete or abandoned.<br><br>I don't remember this happening in other media so it is something that has really come to my attention with anime. But I have been watching a lot of anime recently and it does seem to be a common pattern so i am not sure if it is something I should be concerned about. <br><br>Would be good if someone could explain what is going on here. <br><br>TLDR: An anime has multiple seasons. The first couple of seasons have 24 episodes but the last season only has 12 episodes (so far).