What is the difference between id and user_id

Description
I am trying to understand json data received from hook. Attached the json received for participant_left

  1. What are the id and user_id in object->participant
  2. Are above ids fixed all time?
  3. Is entire meeting start data is duplicated? If so then is there any benefit of tracking meeting_start/meeting_end data? As will get all info using participant joined and left events.
  4. what is uuid?
  5. what is account id?

Which App Type (OAuth / Chatbot / JWT / Webhook)?
Webhook

Which Endpoint/s?
definition of data passed json
{
“event”: “meeting.participant_joined”,
“payload”: {
“object”: {
“id”: “212996017”,
“type”: 2,
"uuid": “4Qa/rGoiTsdas==”,
“topic”: “Learning Workshop”,
“host_id”: “jiCBdpYcxzcsd”,
“duration”: 90,
“timezone”: “Asia/Kolkata”,
“start_time”: “2020-04-11T05:24:56Z”,
“participant”: {
"id": “jiCBdpYpRnuesdfsdfssssuNMg”,
** “user_id”: “16732320”,**
“join_time”: “2020-04-11T05:24:47Z”,
“user_name”: “Stratbeans Consulting”
}
},
“account_id”: “Q_ryUsdfsdfw3Q”
}
}

participant.id === if participant is a registered Zoom User, it is that user’s ID (if they’re logged into Zoom, IIRC)

participant.user_id === participant’s unique identifier for this specific single meeting (this may display as a phone number for dial-in users)

I found some related information in this post that might be helpful: Unable to map meeting registrant id with live participant id

Thanks bdeanindy.
What is meeting type? I always see it to be 2. Are there other types?