Basically a worldwide treasure hunt all over the place. If you want to learn more go to geocaching.com.
People hide containers with a piece of paper that you write your name on after you find it called a logbook. They can also include toys if they are big enough.
You can download the Geocaching app and create an account. After that you can navigate to caches near you. Once you find one, you can go to the geocaching app and log the cache as found.
There are different difficulty and terrain ratings on geocaches. Some are really hard to find, and some are really easy to find.
People that don’t geocache are called muggles. Sometimes a muggle will accidentally stumble upon a cache and they mistake it for trash and it is thrown away.
That’s just scratching the surface of geocaching though.
Check it out at geocaching.com