What does [L before a java class signify

Hi,

I'm using -XX:+PrintClassHistogram to print the number of instances of each class because the application is going OOM. When I take look at the output I see the following class as the one taking the max heap space
num   #instances    #bytes  class name
--------------------------------------
  1:   4497682   534109352  [Ljava.lang.Object;

What does [L prefix to java.lang.Object mean?
Other classes appear without an prefix
e.g
 2:   8639038   207336912  java.lang.Integer

why does java.lang.Object appear with [L as prefix and what does it mean wheres there is no prefix to java.lang.Integer

Thanks