The phrase "opening chapters" refers to the beginning sections of a book or story where the plot and characters are introduced. It is like the starting point or introduction to the whole story. Full definition
You can enable the advanced features of search functions by finding the keyword in open chapters only, look for letters that are case sensitive, and find the whole words only. (bbebooksthailand.com)
Here are 11 tips for creating a strong opening chapter for your book. (tumblr.com)