[DOCS] Document @timestamp as only valid DS timestamp field (#59225)

Author: jrodewig

docs/reference/data-streams/data-streams-overview.asciidoc

@@ -16,9 +16,9 @@ the stream's backing indices. It contains:
 
 * A name or wildcard (`*`) pattern for the data stream.
 
-* The data stream's _timestamp field_. This field must be mapped as a
-  <<date,`date`>> or <<date_nanos,`date_nanos`>> field data type and must be
-  included in every document indexed to the data stream.
+* A mapping for the data stream's `@timestamp` field. This field must be mapped
+as a <<date,`date`>> or <<date_nanos,`date_nanos`>> field data type and must be
+included in every document indexed to the data stream.
 
 * The mappings and settings applied to each backing index when it's created.
 

docs/reference/data-streams/set-up-a-data-stream.asciidoc

@@ -21,11 +21,8 @@ and its backing indices.
 === Prerequisites
 
 * {es} data streams are intended for time-series data only. Each document
-indexed to a data stream must contain a shared timestamp field.
-+
-TIP: Data streams work well with most common log formats. While no schema is
-required to use data streams, we recommend the {ecs-ref}[Elastic Common Schema
-(ECS)].
+indexed to a data stream must contain the `@timestamp` field. This field must be
+mapped as a <<date,`date`>> or <<date_nanos,`date_nanos`>> field data type.
 
 * Data streams are best suited for time-based,
 <<data-streams-append-only,append-only>> use cases. If you frequently need to
@@ -133,17 +130,17 @@ this pattern.
 ----
 ====
 
-* A `data_stream` definition containing the `timestamp_field` property.
-  This timestamp field must be included in every document indexed to the data
-  stream.
+* A `data_stream` definition containing `@timestamp` in the `timestamp_field`
+property. The `@timestamp` field must be included in every document indexed to
+the data stream.
 
 * A <<date,`date`>> or <<date_nanos,`date_nanos`>> field mapping for the
-timestamp field specified in the `timestamp_field` property.
+`@timestamp` field.
 +
-IMPORTANT: Carefully consider the timestamp field's mapping, including
+IMPORTANT: Carefully consider the `@timestamp` field's mapping, including
 <<mapping-params,mapping parameters>> such as <<mapping-date-format,`format`>>.
-Once the stream is created, you can only update the timestamp field's mapping by
-reindexing the data stream. See
+Once the stream is created, you can only update the `@timestamp` field's mapping
+by reindexing the data stream. See
 <<data-streams-use-reindex-to-change-mappings-settings>>.
 
 * If you intend to use {ilm-init}, you must specify the

docs/reference/indices/get-data-stream.asciidoc

@@ -105,15 +105,16 @@ Name of the data stream.
 
 `timestamp_field`::
 (object)
-Contains information about the data stream's timestamp field.
+Contains information about the data stream's `@timestamp` field.
 +
 .Properties of `timestamp_field`
 [%collapsible%open]
 =====
 `name`::
 (string)
-Name of the data stream's timestamp field. This field must be included in every
-document indexed to the data stream.
+Name of the data stream's timestamp field, which must be `@timestamp`. The
+`@timestamp` field must be included in every document indexed to the data
+stream.
 =====
 
 `indices`::