Define respective components of HDFS and YARN

Hadoop Distributed File System, also known as HDFS, Hadoop architecture, Yet Another Resource Negotiator, also known as YARN, and YARN architecture.
Hadoop Distributed File System (HDFS)
HDFS is a distributed file system that provides access to data across Hadoop clusters. A cluster is a group of computers that work together.
Like other Hadoop-related technologies, HDFS is a key tool that manages and supports analysis of very large volumes petabytes and zetabytes of data.
What is YARN?
YARN is the acronym for Yet Another Resource Negotiator. YARN is a resource manager created by separating the processing engine and the management function of MapReduce.
It monitors and manages workloads, maintains a multi-tenant environment, manages the high availability features of Hadoop, and implements security controls
For more details
https://www.simplilearn.com/hdfs-and-yarn-tutorial

Nice detailed here

https://www.quora.com/What-are-HDFS-and-YARN