The following table provides a list of terms commonly used in documentation and conversation around Microsoft Azure cloud services. 

Term to know Description
Azure subscription Subscriptions are used to pay for Azure cloud services. You can have several subscriptions, but it can be difficult to share resources between subscriptions.
Azure tenant An Azure AD tenant is representative of a single organization. It is a dedicated, trusted instance of Azure AD. Tenants can gain access to services in either a dedicated environment (single tenant) or in a shared environment with other organizations (multitenant).
Azure AD directory Each Azure tenant has a dedicated, trusted Azure AD directory that contains the tenant’s users, groups, and applications. It is used to perform identity and access management functions for tenant resources. Because a unique Azure AD directory is automatically provisioned to represent your organization when you sign up for a Microsoft cloud service like Azure, you’ll sometimes see the terms tenant, Azure AD, and Azure AD directory used interchangeably.
Custom domain When you first sign up for a Microsoft cloud service subscription, your tenant (organization) uses an domain name. However, most organizations have one or more domain names that are used to do business and that end users use to access company resources. 
Azure AD account These are identities that are created by using Azure AD or another Microsoft cloud service such as Office 365. They are stored in Azure AD and accessible to any of the organization’s cloud service subscriptions.
Azure subscription administrator The account administrator is the person who signed up for or bought the Azure subscription. They log into  Under the CSP model, any new subscriptions must be requested through the SES portal.
Azure AD Global administrator Azure AD Global administrators have full access to all Azure AD administrative features. The person who signs up for a Microsoft cloud service subscription automatically becomes a global administrator by default. You can have more than one global administrator, but only global administrators can assign any of the other administrator roles to users.
Microsoft account Microsoft accounts provide access to consumer-oriented Microsoft products and cloud services. These identities are created and stored in the Microsoft consumer identity account system run by Microsoft.