docs: provide reply definition

spec/asyncapi.md

@@ -131,7 +131,10 @@ A sender is a type of application, that is sending [messages](#definitionsMessag
 A receiver is a type of application that is receiving [messages](#definitionsMessage) from [channels](#definitionsChannel). A receiver MAY receive from multiple channels depending on the [server](#definitionsServer), protocol, and the use-case pattern. A receiver MAY forward a received message further without changing it. A receiver MAY act as a consumer and react to the message. A receiver MAY act as a processor that, for example, aggregates multiple messages in one and forwards them.
 
 ### <a name="definitionsMessage"></a>Message
-A message is the mechanism by which information is exchanged via a channel between [servers](#definitionsServer) and applications. A message MAY contain a payload and MAY also contain headers. The headers MAY be subdivided into [protocol](#definitionsProtocol)-defined headers and header properties defined by the application which can act as supporting metadata. The payload contains the data, defined by the application, which MUST be serialized into a format (JSON, XML, Avro, binary, etc.). Since a message is a generic mechanism, it can support multiple interaction patterns such as event, command, request, or response. 
+A message is the mechanism by which information is exchanged via a channel between [servers](#definitionsServer) and applications. A message MAY contain a payload and MAY also contain headers. The headers MAY be subdivided into [protocol](#definitionsProtocol)-defined headers and header properties defined by the application which can act as supporting metadata. The payload contains the data, defined by the application, which MUST be serialized into a format (JSON, XML, Avro, binary, etc.). Since a message is a generic mechanism, it can support multiple interaction patterns such as event, command, request, or reply.
+
+#### <a name="definitionsReplyMessage"></a>Reply message
+A reply is a special type of message used in the request-reply interaction pattern and can only be used in combination with a request message. In the request-reply interaction pattern, messages are defined as follows: [Sender](#definitionsSender) sends a request message and waits for a reply message, while [Receiver](#definitionsReceiver) receives the request message and responds with a reply message.
 
 ### <a name="definitionsChannel"></a>Channel
 A channel is an addressable component, made available by the [server](#definitionsServer), for the organization of [messages](#definitionsMessage). [Sender](#definitionsSender) applications send messages to channels and [receiver](#definitionsReceiver) applications receive messages from channels. [Servers](#definitionsServer) MAY support many channel instances, allowing messages with different content to be addressed to different channels. Depending on the [server](#definitionsServer) implementation, the channel MAY be included in the message via protocol-defined headers.
@@ -835,7 +838,7 @@ Field Name | Type | Description
 <a name="operationObjectBindings"></a>bindings | [Operation Bindings Object](#operationBindingsObject) \| [Reference Object](#referenceObject) | A map where the keys describe the name of the protocol and the values describe protocol-specific definitions for the operation.
 <a name="operationObjectTraits"></a>traits | [[Operation Trait Object](#operationTraitObject) &#124; [Reference Object](#referenceObject) ] | A list of traits to apply to the operation object. Traits MUST be merged using [traits merge mechanism](#traits-merge-mechanism). The resulting object MUST be a valid [Operation Object](#operationObject).
 <a name="operationObjectMessages"></a>messages | [[Reference Object](#referenceObject)] | A list of `$ref` pointers pointing to the supported [Message Objects](#messageObject) that can be processed by this operation. It MUST contain a subset of the messages defined in the [channel referenced in this operation](#operationObjectChannel), and MUST NOT point to a subset of message definitions located in the [Messages Object](#componentsMessages) in the [Components Object](#componentsObject) or anywhere else. **Every message processed by this operation MUST be valid against one, and only one, of the [message objects](#messageObject) referenced in this list.** Please note the `messages` property value MUST be a list of [Reference Objects](#referenceObject) and, therefore, MUST NOT contain [Message Objects](#messageObject). However, it is RECOMMENDED that parsers (or other software) dereference this property for a better development experience.
-<a name="operationObjectReply"></a>reply | [Operation Reply Object](#operationReplyObject) &#124; [Reference Object](#referenceObject)  | The definition of the reply in a request-reply operation.
+<a name="operationObjectReply"></a>reply | [Operation Reply Object](#operationReplyObject) &#124; [Reference Object](#referenceObject)  | The definition of the reply part in a request-reply interaction.  When this property is defined, the [messages](#operationObjectMessages) represent request messages in a request-reply interaction.
 
 This object MAY be extended with [Specification Extensions](#specificationExtensions).
 
@@ -965,7 +968,7 @@ bindings:
 
 #### <a name="operationReplyObject"></a>Operation Reply Object
 
-Describes the reply part that MAY be applied to an Operation Object. If an operation implements the request/reply pattern, the reply object represents the response message.
+Describes the reply part that MAY be applied to an Operation Object. If an operation implements the request-reply interaction pattern, this object represents the reply address/channel and the reply message.
 
 ##### Fixed Fields
 
@@ -1190,7 +1193,7 @@ Map describing protocol-specific definitions for a message.
 
 Field Name | Type | Description
 ---|:---:|---
-<a name="messageBindingsObjectHTTP"></a>`http` | [HTTP Message Binding](https://github.com/asyncapi/bindings/blob/master/http/README.md#message) | Protocol-specific information for an HTTP message, i.e., a request or a response.
+<a name="messageBindingsObjectHTTP"></a>`http` | [HTTP Message Binding](https://github.com/asyncapi/bindings/blob/master/http/README.md#message) | Protocol-specific information for an HTTP message, i.e., a request or a reply.
 <a name="messageBindingsObjectWebSockets"></a>`ws` | [WebSockets Message Binding](https://github.com/asyncapi/bindings/blob/master/websockets/README.md#message) | Protocol-specific information for a WebSockets message.
 <a name="messageBindingsObjectKafka"></a>`kafka` | [Kafka Message Binding](https://github.com/asyncapi/bindings/blob/master/kafka/README.md#message) | Protocol-specific information for a Kafka message.
 <a name="messageBindingsObjectAnypointMQ"></a>`anypointmq` | [Anypoint MQ Message Binding](https://github.com/asyncapi/bindings/blob/master/anypointmq/README.md#message) | Protocol-specific information for an Anypoint MQ message.