Java Gargabe Collector type

Given the following Java contained on Red hat 6.x

java -XX:+PrintCommandLineFlags -version
-XX:InitialHeapSize=2147483648 -XX:MaxHeapSize=32037767584 -XX:+PrintCommandLineFlags -XX:+UseCompressedOops -XX:+UseParallelGC
java version "1.7.0_71"
OpenJDK Runtime Environment (rhel-2.5.3.1.el6-x86_64 u71-b14)
OpenJDK 64-Bit Server VM (build 24.65-b04, mixed mode)

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So this version is using Parallel GC by default.

What exactly is Parallel GC (other than a multi-threaded GC)  compared to the other types of GC?

Thanks