I used to call it "the hook" when I was teaching students how to write introductions.
Read this carefully:
http://grammar.ccc.commnet.edu/grammar/intros.htm
The literary term you are referring to is called the "hook" or "attention grabber." It refers to a specific technique used by authors to capture the reader's interest right at the beginning of a story or piece of writing. The purpose of a hook is to create intrigue, draw the reader into the narrative, and make them want to continue reading. A well-crafted hook can take various forms, such as an intriguing statement, a compelling question, a vivid description, or an unexpected event. To identify the hook in a piece of literature, you should carefully analyze the opening lines or paragraphs and examine how the author uses language and storytelling techniques to immediately engage the reader's attention.
