The short answer:
CITO is an acronym for Cache In and Trash Out.
The long answer:
A CITO is a social event for geocachers. Geocachers have several mottoes. Of those mottoes, the most sacred it probably Leave No Trace.
CITOs in the Dallas-Fort Worth area are often hosted by city and state parks. The event is posted on Geocaching.com. Geocachers who wish to support the community while caching post a “will attend.” At the event, the hosts provide trash bags. As caches are sought, trash is picked up.
A CITO event is typically about three hours long. Earth Day is celebrated with a CITO.
In case you’re curious, I have no idea of how to pronounce CITO. All I know is that I love participating!