Plugins are enablers of customization for core Elasticsearch functionality. They work based on scripts, JAR and config files installed on every node in the cluster. Plugins can add mapping types, analyzers, native scripts, discovery options, and many more. Installing Elasticsearch in Liferay required some plugins that are: analysis-icu, analysis-kuromoji, analysis-smartcn, analysis-stempel.
You need to navigate to Elasticsearch Home, enter ./bin/plugin install [plugin-name] and replace [plugin-name] with the name of a particular plugin.