from: https://www.edureka.co/blog/mapreduce-tutorial/

In this MapReduce Tutorial blog, I am going to introduce you to MapReduce, which is one of the core building blocks of processing in Hadoop framework. Before moving ahead, I would suggest you to get familiar with HDFS concepts which I have covered in my previous HDFS tutorial blog. This will help you to understand the MapReduce concepts quickly and easily.