I used the API "_cat/indices?v" to list all indices, and I noticed that the health status of some indices were yellow. I don't understand why the health status were yellow. Could anybody please explain this? Thanks.
bash-4.2# curl http://10.99.68.208:9200/_cat/indices?v
health status index                             uuid                   pri rep docs.count docs.deleted store.size pri.store.size
yellow open   audit-wauiynwo5urarkptmbo5-201807 d6E9b6VoS1qlZ87LeTL0EQ   5   1        100            0    108.7kb        108.7kb
green  open   t-wauiynwo5urarkptmbo5-kibana     Yxaclh2DQ7KfE946gSLYqQ   1   0         28            1     36.7kb         36.7kb