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+---
+title: "Reference: Glossary"
+description: ""
+weight: 10000
+---
+
+# Reference: Glossary
+
+## Blocks storage
+
+Blocks storage is the Mimir storage engine based on the Prometheus TSDB.
+Grafana Mimir stores blocks in object stores such as AWS S3, Google Cloud Storage (GCS), Azure blob storage, or OpenStack Object Storage (Swift).
+For the full list of supported backends and more information, refer to [Blocks storage]({{<relref "./blocks-storage/_index.md" >}})
+
+## Chunk
+
+A chunk is an object containing encoded timestamp-value pairs for one series.
+
+## Churn
+
+Churn is the frequency at which series become idle.
+
+A series become idle once it's no longer exported by the monitored targets.
+Typically, series become idle when a monitored target process or node gets terminated.
+
+## Flushing
+
+Flushing is the operation run by ingesters to offload time series from memory and store them in the long-term storage.
+
+## Gossip
+
+Gossip is a protocol by which components coordinate with the need for a centralized [key-value store]({{<relref "#key-value-store" >}}).
+
+## HA tracker
+
+The HA tracker is a feature of the Grafana Mimir distributor.
+It deduplicates time series received from two or more Prometheus servers that are configured to scrape the same targets.
+To configure HA tracking, refer to [Configure HA deduplication]({{<relref "./operating-grafana-mimir/configure-ha-deduplication.md" >}}).
+
+## Hash ring
+
+The hash ring is a distributed data structure used by Grafana Mimir for sharding, replication, and service discovery.
+Components use a [key-value store]({{<relref "#key-value-store" >}}) or [gossip]({{<relref "#gossip" >}}) to share the hash ring data structure.
+For more information, refer to the [About the hash ring]({{<relref "./architecture/about-the-hash-ring.md" >}}).
+
+## Key-value store
+
+A key-value store is a database that associates keys with values.
+To understand how Grafana Mimir uses key-value stores, refer to [About the key-value store]({{<relref "./architecture/about-the-key-value-store.md" >}}).
+
+## Org
+
+Refer to [Tenant]({{<relref "#tenant" >}}).
+
+## Ring
+
+Refer to [Hash ring]({{<relref "#hash-ring" >}}).
+
+## Sample
+
+A sample is a single timestamped value in a time series.
+
+Given the series `node_cpu_seconds_total{instance="10.0.0.1",mode="system"}` its stream of samples may look like:
+
+```
+# Display format: <value> @<timestamp>
+11775 @1603812134
+11790 @1603812149
+11805 @1603812164
+11819 @1603812179
+11834 @1603812194
+```
+
+## Series
+
+A series is a single stream of [samples]({{<relref "#sample" >}}) belonging to the same metric, with the same set of label key-value pairs.
+
+Given a single metric `node_cpu_seconds_total` you may have multiple series, each one uniquely identified by the combination of metric name and unique label key-value pairs:
+
+```
+node_cpu_seconds_total{instance="10.0.0.1",mode="system"}
+node_cpu_seconds_total{instance="10.0.0.1",mode="user"}
+node_cpu_seconds_total{instance="10.0.0.2",mode="system"}
+node_cpu_seconds_total{instance="10.0.0.2",mode="user"}
+```
+
+## Tenant
+
+A tenant is the owner of a set of series written to and queried from Grafana Mimir.
+Grafana Mimir isolates series and alerts belonging to different tenants.
+To understand how Grafana Mimir authenticates tenants, refer to [About authentication and authorization]({{<relref "./about-authentication-and-authorization.md" >}}).
+
+## Time series
+
+Refer to [Series]({{<relref "#series" >}}).
+
+## User
+
+Refer to [Tenant]({{<relref "#tenant" >}}).
+
+## Write-ahead log (WAL)
+
+The write-ahead Log (WAL) is an append only log stored on disk by ingesters to recover their in-memory state after the process gets restarted.
+For more information, refer to [The write path]({{<relref "./architecture/_index.md#the-write-path" >}}).