Which type of attack floods a network or server with excessive traffic to make it unavailable to legitimate users?

The type of attack that **floods a network or server with excessive traffic to make it unavailable to legitimate users** is called a Denial-of-Service (DoS) attack.

In a Denial-of-Service attack, the attacker sends a huge amount of data or requests to the target, which can be a server, network, or any service, overwhelming its resources such as bandwidth, memory, or processing power. Because of this excessive traffic, the system becomes overloaded and cannot handle legitimate requests effectively, resulting in disruption or complete unavailability of the service for genuine users.

Think of it like a busy road where too many cars suddenly try to pass through a single lane all at once; legitimate travelers (users) can't move smoothly because of the excessive congestion (traffic) intentionally caused by the attacker.