IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.
Plugins are a way to enhance the basic Elasticsearch functionality in a custom manner. They range from adding custom mapping types, custom analyzers (in a more built in fashion), custom script engines, custom discovery and more.
See the Plugins documentation for more.
Intro to Kibana
ELK for Logs & Metrics