Which of the following is characterized by an attacker attempting to map out an organization's staff hierarchy in order to send targeted emails?

Whaling targets high-profile individuals such as executives and senior management by using information gathered from organizational research, including staff hierarchy mapping, to craft convincing fraudulent emails. The deliberate act of mapping the hierarchy to identify and target influential 'big fish' is the defining characteristic of a whaling campaign.

Impersonation involves pretending to be another person or entity, but it does not specifically describe the reconnaissance-driven hierarchical targeting described in the question.

Privilege escalation is a technique where an attacker gains higher access rights on a system than originally authorized, which is unrelated to email-based social engineering.

Spear phishing is targeted email-based phishing toward specific individuals or groups, but whaling is the more precise term when the targeting methodology involves mapping the organizational hierarchy to reach high-level executives.