National Cybersecurity Center

Cybersecurity Glossary

Essential cybersecurity terms with plain-language definitions

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Access Control
Defense & Prevention
Definition

Security measures that regulate who or what can view or use resources in a computing environment. Examples include passwords, biometrics, and role-based permissions.

Botnet
Threats & Attacks
Definition

A network of compromised computers controlled remotely by an attacker, often used to send spam, launch DDoS attacks, or steal data without the owners' knowledge.

Brute Force Attack
Threats & Attacks
Definition

An attack method that tries every possible combination of passwords or encryption keys until the correct one is found. Strong, long passwords make brute force attacks impractical.

Compliance Audit
Compliance
Definition

A formal review to determine whether an organization meets the requirements of regulatory standards such as HIPAA, GDPR, or PCI-DSS. Audits help identify gaps and reduce legal risk.

Data Breach
Threats & Attacks
Definition

An incident where sensitive, protected, or confidential data is accessed, stolen, or exposed by an unauthorized individual. Breaches can result in identity theft and financial loss.

DDoS
Threats & Attacks
Definition

Distributed Denial of Service — an attack that floods a website or service with traffic from many sources simultaneously, overwhelming it and making it unavailable to legitimate users.

Encryption
Defense & Prevention
Definition

The process of converting data into a coded format that can only be read by someone with the correct decryption key. It protects data in transit and at rest.

Endpoint Detection & Response
Defense & Prevention
Definition

A cybersecurity solution that continuously monitors end-user devices (laptops, phones, servers) to detect and respond to threats like malware and ransomware in real time.

Firewall
Defense & Prevention
Definition

A network security system that monitors and controls incoming and outgoing traffic based on predetermined rules. Firewalls act as a barrier between trusted internal networks and untrusted external networks.

GDPR
Compliance
Definition

General Data Protection Regulation — a European Union law that governs how personal data is collected, stored, and processed. It grants individuals rights over their data and imposes strict penalties for violations.

Hacker
General Security
Definition

A person who uses technical skills to gain unauthorized access to systems or networks. Ethical (white-hat) hackers help organizations find vulnerabilities, while malicious (black-hat) hackers exploit them.

HIPAA
Compliance
Definition

Health Insurance Portability and Accountability Act — a U.S. law that sets standards for protecting sensitive patient health information from being disclosed without consent.

Incident Response
Defense & Prevention
Definition

A structured approach to handling security breaches or cyberattacks. The goal is to manage the situation so damage is limited, recovery time is reduced, and costs are minimized.

Keylogger
Threats & Attacks
Definition

A type of surveillance software or hardware that records every keystroke made on a device. Attackers use keyloggers to capture passwords, credit card numbers, and other sensitive information.

Malware
Threats & Attacks
Definition

Malicious software designed to damage, disrupt, or gain unauthorized access to a computer system. Common types include viruses, worms, trojans, ransomware, and spyware.

Man-in-the-Middle Attack
Threats & Attacks
Definition

An attack where a cybercriminal secretly intercepts and possibly alters communications between two parties who believe they are directly communicating with each other.

Multi-Factor Authentication
Defense & Prevention
Definition

A security method that requires two or more forms of verification before granting access — such as a password plus a code sent to your phone. MFA significantly reduces the risk of unauthorized access.

Patch
Defense & Prevention
Definition

A software update released to fix security vulnerabilities, bugs, or performance issues. Applying patches promptly is one of the most effective defenses against known exploits.

Penetration Testing
Defense & Prevention
Definition

A simulated cyberattack performed by security professionals to identify vulnerabilities in a system before malicious hackers can exploit them. Also known as a pen test.

Phishing
Threats & Attacks
Definition

A social engineering attack where attackers send fraudulent messages — typically via email — designed to trick victims into revealing sensitive information or installing malware.

Ransomware
Threats & Attacks
Definition

A type of malware that encrypts a victim's files and demands a ransom payment in exchange for the decryption key. Ransomware can cripple businesses and critical infrastructure.

SIEM
Defense & Prevention
Definition

Security Information and Event Management — a system that collects and analyzes security data from across an organization's IT infrastructure to detect threats and support incident response.

Social Engineering
Threats & Attacks
Definition

Manipulation techniques that exploit human psychology to trick people into giving up confidential information or performing actions that compromise security.

Spyware
Threats & Attacks
Definition

Software that secretly gathers information about a person or organization and sends it to a third party. Spyware can track browsing habits, capture credentials, and monitor activity.

Threat Intelligence
General Security
Definition

Evidence-based knowledge about existing or emerging cyber threats used to inform decisions about how to protect against attacks. It helps organizations anticipate and prepare for threats.

Trojan
Threats & Attacks
Definition

Malware disguised as legitimate software that tricks users into installing it. Once active, trojans can steal data, install additional malware, or give attackers remote access to the system.

VPN
Defense & Prevention
Definition

Virtual Private Network — a service that encrypts your internet connection and routes it through a secure server, protecting your online activity from eavesdropping, especially on public Wi-Fi.

Vulnerability
General Security
Definition

A weakness in a system, application, or process that could be exploited by a threat actor to gain unauthorized access or cause harm. Vulnerabilities are often addressed through patches.

Zero-Day
Threats & Attacks
Definition

A previously unknown software vulnerability that attackers discover before the vendor has released a fix. Zero-day exploits are particularly dangerous because no patch is available yet.

Zero Trust
General Security
Definition

A security framework that requires all users and devices — whether inside or outside the network — to be verified before being granted access. The principle: never trust, always verify.