Copyright law applies to chapter titles within a book in the same way it applies to any other textual work. This means that a chapter title is considered a “literary work” and technically can be copyrighted.
Copyright protects original works of authorship that are tangible and fixed in a tangible form (such as a book, painting, or recording). This means that if someone creates an original title, they can register it with the U.S. Copyright Office to gain exclusive rights to the title. This includes chapter titles. This means that if someone uses this title without permission, they have committed copyright infringement.
However, copyright law is generally based on the originality of the work; titles that are not particularly creative or original are unlikely to be protected by copyright. For example, a chapter title that is simply the name of an object or place won't typically be protected under copyright.
In addition, titles that are not sufficiently “fixed in a tangible form” may not be protected by copyright. This means if a title appears in an ephemeral format (e.g. a Facebook post) or is discussed orally, it may fall outside of copyright protection.
Ultimately, authors should be careful when using chapter titles created by other authors without permission, as this could run afoul of copyright law. If you're unsure about whether or not a particular use of a chapter title requires permission, the best course of action is to consult an attorney.
For more information, please see the U.S. Copyright Office’s copyright basics page: https://www.copyright.gov/circs/circ1.pdf