green belt 
noun
1chiefly British An area of open land around a city, on which building is restricted: Darlington should preserve its green belt...
- In addition, the public generally may be affected if, for example, conservation areas or the green belt is affected.
- The owners of several sites have also carried out changes of use and minor building work on green belt land, without planning permission.
- Little can be built in the grounds of a Grade One listed building and the area is also in a conservation area and green belt.
2A green belt marking a level of proficiency in judo, karate, or other martial arts below that of a brown belt.She's working out her post-dot-bomb angst by training for a green belt in karate.
2.1A person qualified to wear a green belt.Heather was just a green belt; she wouldn't be able to do it.