Not all abbreviations that look alike expand to the same kind of word. Some describe a protocol, a set of rules for communication, while others might describe a unit of data; matching the right word class to the right letter is essential.
UDP stands for User Datagram Protocol. It is a lightweight, connectionless protocol used for sending data, called datagrams, across a network quickly, without the extra overhead of guaranteeing delivery or order, which makes it suitable for tasks like live video or voice calls where speed matters more than perfect reliability.
"User Datagram Packet" and "User Data Packet" incorrectly use "Packet" as the final word, when the standard term is "Protocol", since UDP describes a set of communication rules rather than a single unit of data. "Unique Data Protocol" changes the first word entirely and does not match the accepted expansion.
Contrast UDP with TCP: TCP guarantees delivery and order at the cost of speed, while UDP favours speed and accepts that some data may be lost, which is why the final word in its name is "Protocol", just like TCP.