Spark what is yarn-client mode exactly ?

[zxz]

Apache-spark rencently update the version to 0.8.1, in which yarn-client mode is available. My question is, what is yarn-client mode really mean? In the documentation it says:

With yarn-client mode, the application will be launched locally. Just like running  
application or spark-shell on Local / Mesos / Standalone mode. The launch method is also 
the similar with them, just make sure that when you need to specify a master url, use   
“yarn-client” instead

What dose it mean for "launched locally"? locally where? Spark?
What is the specific differece from the yarn-standalone mode ?

The documentation is not very detailed , any answer or reply is very appriciated,Thanks very much!