Azure tenant is a dedicated and trusted Azure Active Directory's instance.
It is automatically created when your organization signs up for a Microsoft cloud service subscription, such as Microsoft Azure, Microsoft Intune, or Office 365.
An Azure tenant represents a single organization.
Azure tenant is a directory, whereas subscription is an object that represents a "folder" where you can put in your resources.
Subscriptions are tied to tenants. A single tenant can have many subscriptions, but not vice versa is not possible.