Put "dialect" in the spec.

jsonschema-core.xml

@@ -146,6 +146,7 @@
             <t>
                 To facilitate re-use, keywords can be organized into vocabularies.  A vocabulary
                 consists of a list of keywords, together with their syntax and semantics.
+                A set of vocabularies identified by a meta-schema is known as a dialect.
             </t>
             <t>
                 JSON Schema can be extended either by defining additional vocabularies,
@@ -173,7 +174,9 @@
             </t>
             <t>
                 Further vocabularies for purposes such as structural validation or
-                hypermedia annotation are defined in other documents.
+                hypermedia annotation are defined in other documents.  These other
+                documents each define a dialect collecting the standard sets of
+                vocabularies needed to write schemas for that document's purpose.
             </t>
         </section>
 

jsonschema-validation.xml

@@ -177,9 +177,10 @@
 
         <section title="Meta-Schema" anchor="meta-schema">
             <t>
-                The current URI for the default JSON Schema meta-schema is
+                The current URI for the default JSON Schema dialect meta-schema is
                 <eref target="https://json-schema.org/draft/2019-09/schema"/>.
-                For schema author convenience, this meta-schema describes all vocabularies
+                For schema author convenience, this meta-schema describes a dialect
+                consisting of all vocabularies
                 defined in this specification and the JSON Schema Core specification,
                 as well as two former keywords which are reserved for a transitional period.
                 Individual vocabulary and vocabulary meta-schema URIs are given for