The description of those fields can be found here: http://help.adobe.com/en_US/adobemediaserver/adminapi/WSa4cb07693d1238 8431df580a12a34991ebc-8000.2.3.html#WS5b3ccc516d4fbf351e63e3d11a0d3ed9 99-7fe5AdminAPI.2.3
Number; total number of segment “hits” since the server started.
Number; total number of segment misses since the server started.
"If requested data is contained in the cache (cache hit), this request can be served by simply reading the cache, which is comparatively faster. Otherwise (cache miss), the data has to be recomputed or fetched from its original storage location, which is comparatively slower. Hence, the greater the number of requests that can be served from the cache, the faster the overall system performance becomes." -- The all knowing Wikipedia