Answer + Explanation:
The Glass Castle is a "memoir" because of the following:
Definition of Memoir: a collection of memories that an individual writes about moments or events, both public or private, that took place in the subject's/person’s life
The Glass Castle includes: details her unconventional childhood growing up with an alcoholic father and a mother who seems to be mentally ill
The Glass Castle contains a collection of memories that took place in Jeanette Walls life. The collection of memories are moments and events of how she grew up with her alcoholic father and a seemingly mentally ill mother.