The host key is useful if you set up a meeting and want someone else to be able to join your meeting and become the host while you're not present. A Zoom meeting can only have one host, so you cannot use the host key if someone else in the meeting is already a host but can ask them to make you a co-host.
Note that your host key can be used to become host in any of your Zoom meetings, so be careful who you share your host key with.
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