A protocol that is just spamming. It will send data packets over without caring whether the guy on the other ends even receives it.
We use this if we need data sent FAST. For high frequency data, such as LiDAR scans, if we lose a frame we don't really care since we can have the next one in no time.
Another important thing to know is that for UDP, information (if too large) is split up into packets and sent one at a time. For example, LiDAR scans' might be too large to send over as a packet, therefore it will be split up into many different packets. TCP will not split it up.