Apache Hadoop NextGen MapReduce (YARN) hadoop-0.23 and we now have, what we call, MapReduce 2.0 (MRv2) or YARN.

The fundamental idea of MRv2 is to split up the two major functionalities of the JobTracker,
resource management
and job scheduling/monitoring, into separate daemons.

The idea is to have a
global ResourceManager (RM) and
per-application ApplicationMaster (AM).

An application is either a single job in the classical sense of Map-Reduce jobs or a DAG of jobs.


YARN
http://hadoop.apache.org/docs/r0.23.0/hadoop-yarn/hadoop-yarn-site/YARN.html