The Elasticsearch architecture is quite simple to understand and it is important for you to understand its various terminology in detail before we explain its simple working. This section aims at explaining its terminologies. It's quite hard to go through these terminologies in order as these terminologies get used when we talk about a term interchangeably. Rest assured, keep reading and at the end of these sections, you will have a clear grasp of all terms and this is quite important for understanding the rest of the chapter.