What is an attempt to disrupt the normal functioning of targeted servers or networks by overwhelming them with traffic?

The scenario described refers to a Distributed Denial of Service (DDoS) Attack. In a DDoS attack, an attacker uses multiple systems to flood a target server or network with an overwhelming amount of traffic. This surge in traffic makes the targeted resources unavailable to legitimate users, effectively disrupting normal operations.

DDoS attacks are particularly dangerous because they often involve large botnets made up of compromised devices, which can multiply the attack's impact. By coordinating numerous requests from various sources, the attack can bypass some of the defenses that a single source might encounter. The primary goal is to render the service or resources inaccessible, which is directly aligned with the definition provided in the question.

The other types of attacks listed have different objectives and mechanisms. Brute force attacks aim to gain unauthorized access by repeatedly guessing credentials, phishing attacks involve tricking individuals into providing personal information, and SQL injection exploits vulnerabilities in a database layer of an application to manipulate queries. Each serves a different purpose in the cybersecurity landscape and does not focus on overwhelming a system with traffic.