DDoS (Distributed Denial of Service) - Aderivative of a dos attack in which multiple hosts in multiple locations all focus on one target to reduce its availability to the public.
DOS (denial of service) - a type of attack that prevents any users - even legitimate ones - from using a system.
Mac (media access control) - a sublayer of the data link layer of the OSI (open systems interconnection) model that controls the way multiple devices use the same media channel. This is a communication protocol, not an attack.
ARP(address resolution protocol) used to map known IP addresses to unknown physical addresses. this is a communication protocol commonly used by routers.