edu-30: update docs per edu findings (part2)

doc/user/content/concepts/sources.md

@@ -12,42 +12,14 @@ aliases:
 
 ## Overview
 
-Sources describe external systems you want Materialize to read data from, and
-provide details about how to decode and interpret that data. A simplistic way to
-think of this is that sources represent streams and their schemas; this isn't
-entirely accurate, but provides an illustrative mental model.
-
-In terms of SQL, sources are similar to a combination of tables and
-clients.
-
-- Like tables, sources are structured components that users can read from.
-- Like clients, sources are responsible for reading data. External
-  sources provide all of the underlying data to process.
-
-By looking at what comprises a source, we can develop a sense for how this
-combination works.
-
-[//]: # "TODO(morsapaes) Add details about source persistence."
-
-## Source components
-
-Sources consist of the following components:
-
-Component      | Use                                                                                               | Example
----------------|---------------------------------------------------------------------------------------------------|---------
-**Connector**  | Provides actual bytes of data to Materialize                                                      | Kafka
-**Format**     | Structures of the external source's bytes, i.e. its schema                                        | Avro
-**Envelope**   | Expresses how Materialize should handle the incoming data + any additional formatting information | Upsert
+{{% include-headless "/headless/source-definition" %}}
 
 ### Connectors
 
 Materialize bundles native connectors for the following external systems:
 
 {{< include-md file="shared-content/multilink-box-native-connectors.md" >}}
 
-For details on the syntax, supported formats and features of each connector, check out the dedicated `CREATE SOURCE` documentation pages.
-
-
 ## Sources and clusters
 
 Sources require compute resources in Materialize, and so need to be associated

doc/user/content/headless/source-definition.md

@@ -0,0 +1,14 @@
+---
+headless: true
+---
+A source in Materialize represents an external data source. More concretely, it
+specifies the connection and the ingestion configuration to use for a particular
+external data source (e.g., PostgreSQL, Kafka). For those familiar with
+PostgreSQL's foreign servers and foreign tables, a source is like a foreign
+server, and the tables (or subsources) created from the source are like foreign
+tables.
+
+Before creating a source in Materialize, you must ensure that the external data
+source is properly configured and accessible so that Materialize can establish a
+connection and ingest its data. The exact configuration depends on the type of
+data source.

doc/user/content/sql/create-source/_index.md

@@ -8,7 +8,7 @@ menu:
     identifier: 'create-source'
 ---
 
-A [source](/concepts/sources/) describes an external system you want Materialize to read data from, and provides details about how to decode and interpret that data.
+{{% include-headless "/headless/source-definition" %}}
 
 ## Syntax summary