A sequel is a story, book, or movie that comes after another story, book, or movie. The opposite is a prequel. A combination of the two makes a midquel. When there are many sequels, this is called a series.
A sequel has important parts of the first story like characters and places. Audiences like sequels because they have more of the characters and places they like. Storytellers and publishers like sequels because they are popular and people buy them.
Sequel names are often similar to the name of a first story or other stories in a series. They often have a second title or a number to show that they are alike or different from a first story or other stories in a series. Sometimes sequels have different names in different countries because they mean different things to different audiences.