what does the event dispatcher listen timer mean?

I have a Standard RAC database version 11.2.0.3 with 2 instances. Database hasn't had MTS configuration. But on the staspack report this event appears constantly with a high percentage.

Could you tell me what this wait event could mean? I cannot find information on the Metalink, Oracle documentation, etc

Top 5 Timed Events	Avg %Total
~~~~~~~~~~~~~~~~~~	wait   Call
Event	Waits	Time (s)   (ms)   Time

----------------------------------------- ------------ ----------- ------ ------

PL/SQL lock timer	1,350	2,701   2000   49.5
dispatcher listen timer	15	900  60012   16.5
db file sequential read	73,821	864	12   15.8
read by other session	71,945	850	12   15.6
direct path write temp	2,913	29	10	.5
	-------------------------------------------------------------

Thanks