title: What does the "shared memory zone" mean in nginx?
body: <p>According to the nginx documentation, the <a href="http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_cache_path" rel="noreferrer">proxy_cache_path</a> directive has a parameter called <code>keys_zone</code>. The documentation also refers a concept of "shared memory zone".</p>
  
  <blockquote>
    <p>In addition, all active keys and information about data are stored in a shared memory zone, whose name and size are configured by the keys_zone parameter. One megabyte zone can store about 8 thousand keys.</p>
  </blockquote>
  
  <p>Is the "shared memory zone" a general term? or a specific term used by nginx? What does the "shared" exactly mean?</p>