Hi FOR365,
Environment is the new name for instances. An environment is a space to store, manage, and share your company's business data, apps, and flows. You can learn about creating and managing environments in the Power Platform admin center here.
Organization is another name for tenant, as well as the name of an entity. A tenant is the account you create in the Microsoft Online Services environment (such as Office 365) when you sign up for a subscription. A tenant contains uniquely identified domains, users, security groups, and subscriptions. A tenant can include one or more environments; however, an environment is always associated with a single tenant. You can read more about tenants here.
