A Zoom Meeting/Webinar ID is the meeting number assigned to each Zoom meeting and can be a 10 or 11 digit number.  Meet Now (Instant Meetings), Scheduled Meetings (which may also be used as recurring meetings), and Webinar IDs contain 11 digits, while a Personal Meeting ID (also referred to as PMI) contains 10 digits. 
Please note: Meetings scheduled prior to April 12, 2020, may have a Meeting ID that is 9 digits.

Meeting ID Expirations

• Meet Now (Instant Meetings) meeting IDs expire when the meeting ends
• A Scheduled (non-recurring) meeting ID will expire 30 days after the meeting is scheduled for (unless the meeting was recorded). You can restart the same meeting ID as many times as you would like, within the 30-day period. If you do reuse the meeting ID during that 30 day period, it will allow for the meeting ID to be used for an additional 30 days (you may keep doing this).
• Recurring meeting IDs expire after 365 days from the last date it was used
• Webinar IDs will expire and be unusable past the webinars scheduled end-time if the webinar is not currently in progress. The webinar will be deleted from previous webinars 30 days after the scheduled end time.

More information about Meeting/Webinar IDs can be found here.