Docker (www.docker.com) is a company who has been a major force behind popularizing containerization of applications. Docker is to containers what Google is for search. Sometimes, people even use containers and Docker as synonyms. Microsoft has partnered with docker and is actively contributing to the docker platform and tools in open source. This makes docker important for us as .NET developers.
Docker is a very important topic and will be significant enough to learn for any serious .NET developer. However, due to time and scope constraints, we will just scratch the surface of the ecosystem of docker here. We strongly recommend that you read through the Docker books made available by Packt Publishing.
Now let's focus on some of the terminologies...