Unicast refers to a protocol that is a one to one connection between a master and the slave or server and client.
These devices will send packets to each other back and forth directly.
The protocol will be using some tags and encryptions in its code which can be used to identify the source and destination of the packets. Precision Time Protocol is one of the protocols that are capable of acting as a unicast protocol.
The key advantages of using Unicast protocols includes the ability to ensure that only the intended recipient should receive a packets from a verified source.