- **`name`**: Name that identifies this topic instance uniquely. Refer to *[../../type/basic.json#/definitions/entityName](#/../type/basic.json#/definitions/entityName)*.
- **`description`**: Description of the topic instance. What it has and how to use it. Refer to *[../../type/basic.json#/definitions/markdown](#/../type/basic.json#/definitions/markdown)*.
- **`service`**: Fully qualified name of the messaging service where this topic is hosted in. Refer to *[../../type/basic.json#/definitions/fullyQualifiedEntityName](#/../type/basic.json#/definitions/fullyQualifiedEntityName)*.
- **`messageSchema`**: Refer to *[../../type/schema.json](#/../type/schema.json)*.
- **`retentionSize`** *(number)*: Maximum size of a partition in bytes before old data is discarded. For Kafka - `retention.bytes` configuration. Default: `"-1"`.
- **`topicConfig`**: Contains key/value pair of topic configuration. Refer to *[../../entity/data/topic.json#/definitions/topicConfig](#/../entity/data/topic.json#/definitions/topicConfig)*.
- **`owners`**: Owners of this topic. Refer to *[../../type/entityReferenceList.json](#/../type/entityReferenceList.json)*. Default: `null`.
- **`tags`** *(array)*: Tags for this topic. Default: `null`.
- **Items**: Refer to *[../../type/tagLabel.json](#/../type/tagLabel.json)*.
- **`extension`**: Entity extension data with custom attributes added to the entity. Refer to *[../../type/basic.json#/definitions/entityExtension](#/../type/basic.json#/definitions/entityExtension)*.
- **`sourceUrl`**: Source URL of topic. Refer to *[../../type/basic.json#/definitions/sourceUrl](#/../type/basic.json#/definitions/sourceUrl)*.
- **`domain`** *(string)*: Fully qualified name of the domain the Topic belongs to. Refer to *[../../type/basic.json#/definitions/fullyQualifiedEntityName](#/../type/basic.json#/definitions/fullyQualifiedEntityName)*.