Which of the following best defines 'alters any writing without one's authority'?

The term "alters any writing without one's authority" is best defined as forgery. Forgery specifically involves the unauthorized alteration or creation of a document with the intent to deceive or defraud someone. This can include changing the contents of a document, signing someone else's name without permission, or creating a false document that appears genuine. The key element here is the unauthorized action, which aligns directly with the definition of forgery.

Fraud, while it may involve deception, generally pertains to dishonest practices to secure an unfair or unlawful gain and may not specifically involve the alteration of a document. Impersonation refers to pretending to be someone else, which can be a separate offense and does not inherently require altering writings. Theft involves taking someone else's property without permission, which does not necessarily include any changes to documents. Thus, the focus on unauthorized alteration makes forgery the most accurate definition in this context.