Add linked terms

x-pack/plugins/monitoring/dev_docs/reference/terminology.md

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+# Terminology
+
+#### Internal collection
+
+The process of collecting monitoring data handled by the stack components themselves. Each component is responsible for sending documents to elasticsearch directly.
+
+#### Metricbeat collection
+
+The process of collecting monitoring data using metricbeat. Each component exposes an endpoint that metricbeat queries using a module for that component. Metricbeat then sends the data to elasticsearch for all monitored components.