What is Docker

Docker is one of container implementation. Others are Rocket, Drawbridge, LXC.
Docker Inc. is the company that sells the commercial version of Docker. Docker is also available as open source.
Docker Daemon / dockerd? Manages Docker objects(Eg: Images, containers, networks, and volumes). dockerd also communicate with other daemons to manage Docker services.
Docker client / docker? Users interact with docker client.

            User 
            $ docker run -----> [Docker Client] -----> [Docker Daemon/dockerd]
        

Docker vs Kubernets

Docker Kubernetes(Container Orchestration system)
What Platform for building containers Platform for managing multiple containers
Use case Run containers on 1 host Run containers on cluster of machines, providing scaling, self-healing, and rollback
Commands docker run helm