hills and fields; countryside
Refers to natural, undeveloped areas outside the city; often used in contexts of nature, hiking, or rural scenery.
I like walking in the hills and fields on weekends.
It's the season when the greenery of the countryside is beautiful.
I like walking through the hills and fields on my days off.
When spring comes, flowers bloom in the hills and fields.
When I was a child, I used to run around playing in the hills and fields.
自然 is the broad word for nature in general, covering plants, animals, and scenery, whereas 野山 specifically means the hills and fields of a landscape.
都会 means a city or urban area, the opposite of the natural hills and fields described by 野山.
野原 means an open field or plain, a flatter area, while 野山 includes hilly terrain along with fields.
Compound of 野 (の, 'field, plain') and 山 (やま, 'mountain, hill'). The combination straightforwardly denotes open fields and hills.