An Access Control List (ACL) is a technical mechanism used to explicitly define permissions for files, folders, or other resources. ACLs specify which users or system processes are granted access to objects and what operations are allowed on given objects. This allows the administrator to centrally and granularly manage file permissions for a group or team.
Reference:
CompTIA Security+ SY0-701 Official Study Guide, Domain 3.1, "Access control lists (ACLs) are used to explicitly define permissions to files and resources for users and groups." Exam Objectives 3.1: "Implement secure network architecture concepts."

ARP poisoning(also known as ARP spoofing) is a basicman-in-the-middle (MITM)attack that involves sending fake ARP responses to redirect traffic. This technique isnot sophisticatedand can be easily executed using freely available tools like Cain & Abel, Ettercap, or Wireshark.
Such attacks are often attempted byunskilled attackers (script kiddies)testing their abilities, especially in environments like schools. The term"unskilled attacker"fits best here, as credential stuffing and DMARC are unrelated to ARP poisoning.
Reference: CompTIA Security+ SY0-701 Objectives, Domain 2.1 - "Attack techniques: MITM, ARP poisoning; attacker types: Unskilled/script kiddie."