What is Docker?
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Quick Answer
Docker is a platform for building, shipping, and running applications in containers — lightweight, isolated units that package an app with its dependencies so it runs the same everywhere.
Detailed Answer
Containers share the host kernel but isolate processes, filesystem, and network via namespaces and cgroups, making them far lighter than VMs. Docker standardized the image format and tooling, solving works on my machine by shipping the runtime environment with the app.
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Interview Tip
Contrast containers with VMs (share the kernel, no full guest OS) — it shows you understand why containers are lightweight.
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