TopicID

TopicID is the Hedera protobuf identifier for a Hedera Consensus Service topic, addressed by shard, realm, and topic number for message submission.

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).