Genres and Topics
These - mostly Sci-Fi movies - are typically set in a post-apocalyptic future in which the world has either been destroyed or is suffering the consequences of a nuclear war, a pandemic, an extraterrestrial attack, an impact event, a cybernetic revolt, etc. They do not necessarily take place on Earth. Please note that there is a related topic - "Nuclear Holocaust".
Topics are sub-genres and/or themes of any kind (romantic comedy, buddy, sports, etc.) that describe the plot of the movie you are looking for. Topics, however, are not keywords. If you search for a topic like "shark", for example, only movies in which sharks play a significant roll will appear, such as 'Jaws'. But not every movie that has a shark in it will be listed.