What is meant by Unicast, Multicast, and Broadcast communications over a TCP/IP network?

These three terms describe how many devices on a network receive a given message:

• Unicast — a message sent from one device to exactly one other device. This is the most common traffic pattern (e.g., a PLC responding to a single SCADA client).
• Multicast — a message sent from one device to a defined subset of devices that have subscribed to receive it, while the rest of the network ignores it. Common in industrial protocols like EtherNet/IP for I/O data shared among specific controllers.
• Broadcast — a message sent from one device to every device on the local network segment, whether they need it or not. Useful for discovery (e.g., ARP requests, DHCP), but excessive broadcast traffic can congest a network .