Terminology explanation and getting started with geohash about geohash-java

[kungfoo]

You best start here: https://en.wikipedia.org/wiki/Geohash
The library is an implementation of this http://geohash.org/

A geohash is not a point, but rather a bounding box defined by subdividing a coordinate system in terms of it's axes.
Two of those bounding boxes are adjacent, if they are next to each other in at least one dimension (for WGS84-coordinates, there is two latitude and longitude).

Precision is actually the size of the bounding box. Less precision means a larger bounding box. The point is (no pun intended) that the prefix of a larger bounding box, that contains another smaller bounding box is the same, so you can check contains() by looking at the prefixes of the hashes.