According to Groundspeak:
A Trackable is a sort of physical geocaching "game piece." You will often find them in geocaches or see them at geocaching gatherings. Each Trackable is etched with a unique code that can be used to log its movements as it travels in the real world. Some of these items have traveled hundreds of thousands of miles thanks to geocachers who move them from cache to cache!
Trackables can be geocoins or travel bugs. A cacher will purchase a trackable with a unique tracking code, often attach it to another item (called a "hitchhiker"), and drop it into a cache with a mission. Most commonly, the mission will be "to go as far as possible". Then, when the next cacher finds it in a cache, they will pick it up and move it along to another cache. Because of the unique tracking code, every movement is logged online and anyone can watch the progress of the item.
|This giant Peeps mission is to attend wherever cachers meet|
|My trackable in the Czech Republic.|
|An example of a "geocoin". Pretty, isn't it?|
|This is my Ginger - I released it in Canada|
|This moose wanted to return to Marquette, Michigan where its owner went to college|
|This is an example of a "travel bug" with many "hitchhikers" attached.|
|Beautiful geocoin from Great Britain.|
|You can attach a trackable to anything|
|My favorite trackable. I moved it from Michigan to Ohio for its owner.|
|Often, TB owners will ask you to take pictures of their trackables with local landmarks|
|This one has been on the move since 2007|
|This one wants to re-join a matching trackable released at the same time|
|Because coins often go missing, many people collect and don't release geocoins|
|Little mouse traveled from England in memory of its late owner|
It's great to know that, even as I'm tucked at home avoiding the rain, my trackables are out there exploring the world and reporting back to me!