Client ZWAVE_GATEWAY-Mosquitto disconnected

I was checking my logs and found this. Can someone tell me what this means ?
The truth is that I don’t even know what Mosquito is and does. Do I even need Mosquito ?

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2023-09-20 19:29:40: Client ZWAVE_GATEWAY-Mosquitto disconnected, not authorised.
2023-09-20 19:29:43: New connection from 172.30.33.1:57384 on port 1883.
error: received null username or password for unpwd check
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