What is docker, briefly:
Docker is a platform that allows developers to package applications into containers—lightweight, portable units that include everything needed to run the software, such as code, libraries, and dependencies. Containers ensure that an application works consistently across different environments, from development to production. Unlike traditional virtual machines, Docker containers share the same OS kernel, making them more efficient and faster to start.

For beginners, Docker simplifies app deployment, letting you focus on writing code rather than worrying about compatibility issues. It’s widely used for microservices, DevOps, and cloud-native applications.