Anypoint MQ Glossary | MuleSoft Documentation
# Anypoint MQ Glossary 

ACK/NACK
    
Operations that specify:
  * ACK operation - An app receives a message, and Anypoint MQ deletes the message.
  * NACK operation - An app does not receive a message, and Anypoint MQ doesn’t delete the message.


For information, see ACK and NACK Operations. 

Binding
    
A method for specifying a set of standard queues that form a message exchange, enabling apps to send messages to multiple queues.
When you specify which message queues are bound to a message exchange, Anypoint MQ creates and manages the bindings for you.
For information, see Sending Messages to Multiple Queues Using Message Exchanges. 

Dead Letter Queue (DLQ)
    
A queue that stores undeliverable messages from other queues.
For information, see Dead Letter Queues. 

Default Acknowledgement Timeout
    
The period that a message remains unacknowledged before being returned to the queue, for example, if a server fails or if flow processing takes too long and times out. 

Delay Queue
    
A queue that postpones delivery of new messages for a specified period.
Consumers can’t see messages sent to a delay queue for the delay duration. The minimum delay for a queue is 0 seconds. The maximum is 15 minutes.
If you change the queue delay for a:
  * Standard queue, the setting change doesn’t affect messages in the queue.
  * FIFO queue, the setting change is retroactive to all messages in the queue.


You can override the default queue delay for a particular message in a standard queue only. 

Delayed Message Delivery
    
A setting that specifies how long to postpone delivery of a particular message to a standard queue.
Consumers can’t see messages sent with delivery delay for the delay duration. The minimum delivery delay for a message is 0 seconds. The maximum is 15 minutes.
FIFO queues don’t support delayed delivery for individual messages. 

Destination
    
A message exchange or queue.
Applications register to a destination and publish messages to that destination. Applications subscribe to a destination to receive a message. Anypoint MQ lets you configure destinations by creating or maintaining queues or message exchanges. You configure destinations in Anypoint Studio using Anypoint MQ Connector. 

Durable Message
    
A message that persists until its target client receives it. 

Duration
    
The period during which messages can persist in flight (for up to two weeks), after Anypoint MQ deletes them. 

Encrypted Queue
    
A queue that is encrypted, enabling companies to comply with their data at rest policies. Use encrypted queues for enhanced security.
If you configure Anypoint MQ queues for encryption at rest, the payloads are encrypted with the AES-256 GCM algorithm on the server side.
Anypoint MQ encrypts only the message body. Anypoint MQ does not encrypt the `headers` or `properties` of messages sent to exchanges and queues. 

Failover
    
A feature that, when enabled for standard queues, assigns a fallback queue in a fallback region. If an application can’t reach the Anypoint MQ server in the primary region, the connector automatically diverts message processing to the fallback region.
For information, see Configuring Cross-Region Failover for Standard Queues. 

Fallback Queue
    
A queue that Anypoint MQ automatically creates in a fallback region when failover is enabled for a standard queue. The Anypoint MQ server manages fallback queues and regions; end users can’t configure them.
For information, see Configuring Cross-Region Failover for Standard Queues. 

Fallback Region
    
A region that Anypoint MQ automatically assigns to a fallback queue when failover is enabled for a standard queue. The Anypoint MQ server manages fallback queues and regions; end users can’t configure them.
For information, see Configuring Cross-Region Failover for Standard Queues. 

FIFO Queue
    
A queue that processes messages first-in, first-out (FIFO), ensuring message ordering for applications in which the order of messages must be strictly preserved and enforced.
For information, see FIFO Queues. 

In-Flight
    
Messages that are any of these states:
  * Received by a queue, but not deleted
  * Awaiting acknowledgment (ACK) or not acknowledgment (NACK)
  * Not returned to the queue due to an expired **Default Acknowledgement Timeout** (time-to-live) setting


In-flight messages are not visible to other consumers.
Anypoint MQ supports up to 120,000 in-flight messages per queue for standard (non-FIFO) queues. FIFO queues can have up to 10 in-flight messages in each message group. 

In Queue
    
Messages that have been sent.
Anypoint MQ supports unlimited messages in queue for both standard and FIFO queues. 

Lock ID
    
An identifier that allows only a single app to read a queue. Anypoint MQ provides the lock when an app acknowledges a message from a queue. 

Message
    
Serializable Mule Message content that applications send and receive so that they can communicate with each other. 

Message Exchange
    
A pub/sub message source with multiple outputs. Applications register to subscribe to messages that the message exchange publishes.
For information, see Sending Messages to Multiple Queues Using Message Exchanges. 

Message Groups
    
An assignment of specific messages to a group, enabling multiple consumers to process messages from a single FIFO queue.
For information, see FIFO Queues and Message Groups. 

Message-Routing Rules
    
Rules that you configure on a message exchange binding to route a subset of the messages published to an exchange to a specific queue. 

On-premises
    
Mule runtime that runs on a computer in your organization. 

Payload
    
The message content, which can be text, JSON, or CSV (comma-separated values). 

Point-to-Point
    
A pattern that allows an app to send a message that only a single app can receive. 

Pub/Sub (Publish/Subscribe)
    
A pattern that distributes messages to multiple consumers. 

Publisher
    
An app that sends messages to Anypoint MQ. 

Queue
    
A point-to-point message storage area that holds a message that a client receives.
For information, see Configuring and Using Queues. 

Subscriber
    
An app that receives messages from Anypoint MQ. 

TTL (time-to-live)
    
How long the message stays in a queue before Anypoint MQ expires and removes it from the queue.
Each queue has a message time-to-live (TTL).
If you change the message TTL for a queue, the new TTL value applies to any messages in the queue and all new messages added to the queue.
## See Also
  * Anypoint MQ Overview
  *