Wikipedia says ...
Field recording is the technique for capturing the audible illustration of an environment, produced outside of a recording studio. A "field recording" is the actual recording that is produced. Field recording, sometimes called Phonography, was originally employed as a documentary adjunct to research work in the field, but has since also found use as evocative art in itself.
I love hunting for unusual sounds, and the world is full of them. Open ears are all you need.