A container is an isolated runtime package that bundles an application with the libraries, tools, and settings it needs to run. Unlike a full virtual machine, a container shares the host kernel while separating processes, filesystems, and network settings to a limited degree. That makes containers lightweight and easy to move between systems, which is why they are common in development, testing, and deployment.
In cybersecurity, containers matter because isolation is helpful but not absolute. A poorly configured container can expose host files through mounts, leak credentials from environment variables, or reach internal services it should not access. Attackers may abuse trusted images, weak permissions, or overbroad mounts to move from a container into sensitive data or adjacent systems. Defenders reduce risk by using trusted images, least-privilege settings, read-only mounts where possible, secret management, image scanning, and logging that shows what each container can access.