diff --git a/docs/content/Concepts-and-Terminology.md b/docs/content/Concepts-and-Terminology.md
index 21f62288f8e..c6b92a876d0 100644
--- a/docs/content/Concepts-and-Terminology.md
+++ b/docs/content/Concepts-and-Terminology.md
@@ -16,6 +16,8 @@ More definitions are available on the [design page](Design.html).
 
 * **Dimensions** Aspects or categories of data, such as languages or locations. For example, with *language* and *country* as the type of dimension, values could be "English" or "Mandarin" for language, or "USA" or "China" for country. In Druid, dimensions can serve as filters for narrowing down hits (for example, language = "English" or country = "China").
 
+* **Ephemeral node** A Zookeeper node that exists only for the time it is needed to complete the process for which it was created. Different types of Druid nodes may create ephemeral nodes as part of their work.
+
 * **Granularity** The time interval corresponding to aggregation by time. Druid configuration settings specify the granularity of [timestamp](#timestamp) buckets in a [segment](#segment) (for example, by minute or by hour), as well as the granularity of the segment itself. The latter is essentially the overall range of absolute time covered by the segment. In queries, granularity settings control the summarization of findings.
 
 * **Ingestion** The pulling and initial storing and processing of data. Druid supports realtime and batch ingestion of data, and applies indexing in both cases.