TopicID

Hedera protobuf reference for the TopicID message, a unique identifier used by the Hashgraph consensus service to address a topic by shard, realm, and number.

Unique identifier for a topic (used by the consensus service)

Field	Description
shardNum	The shard number (nonnegative)
realmNum	The realm number (nonnegative)
topicNum	Unique topic identifier within a realm (nonnegative).