What means when an iPhone lock on iCloud

That means when an iPhone lock on iCloud

It means the iPhone the previous owner of the phone has its iCloud account linked to the phone, basically, the iPhone can not be used unless the previous owner removes from “Find My iPhone”, to do so:

1. Sign in to iCloud.com with their Apple ID.
2. Go to Find My iPhone.
3. Click All Devices at the top of the screen.
4. Select the device that you want to remove from iCloud.
5. If necessary, click Erase [device].
6. Click Remove from Account.