It's a layer 4 protocol of OSI. It's much lighter than TCP.
- Smaller Packets - less bandwidth
- Fast - due to less features and smaller packets
- Stateless - no connection needed, sender just sends data. If the server restarts, it will continue receiving the data.
- No Acknowledgment - the sender does not know if the receiver received the bytes. Hence, there's no delivery guarantee
- No Congestion Control - UDP will send packets no matter what the traffic is
- No Ordering - packets may be received out of order
- Low Security - due to connectionless nature, receiver does not know anything about the sender. Some firewalls disable UDP due to it.