Words we use

Zappocity and Mailocity share their customers, so the panels, the command line and these articles use five words, each for one thing.

Word	What it is	Where you see it
Organization	A Zappocity customer: it pays (subscriptions, invoices, credit) and has members. A company, or one person's own (personal).	Zappocity panel, Customers
Person	Someone who signs in with a zappo.city account (an email and password, two-step sign-in). Has a customer number such as C-1042.	Zappocity panel, Customers → People
Member	A person in an organization, with one of six roles: owner, admin, billing, support, member or guest.	An organization's Members
Tenant	A Mailocity customer: its domains, mailboxes, aliases, lists and settings. Each tenant belongs to one organization, which pays for it.	Mailocity panel, Tenants; the tenant manager
Mailbox	An email address that receives mail, in a tenant. Its owner is a person, who signs in to it through zappo.city; a shared mailbox has no owner of its own.	A tenant's Mailboxes; Zappocity panel, Mailboxes

How they fit:

An organization has one tenant (or more) on Mailocity. Its name and the tenant's follow each other when it has one.
Everyone with a mailbox in a tenant is a member of its organization, with the mailbox's role; a role changed on either side reaches the other within a minute (see Members, roles and names stay the same). Members without a mailbox (a bookkeeper with the billing role, say) are allowed.
A person may own mailboxes in several tenants, and sign in to each with one zappo.city account.

Older words you may still meet:

Team was a tenant: the tenant manager was the "team manager", and some customer pages (signing up, joining, webmail) still say team.
User was a mailbox: corpsuite user ... still works for corpsuite mailbox ....
Account is a mailbox in the admin API (/v1/tenants/{tenantId}/accounts), and a Zappocity account is a person.
The admin API keeps /v1/tenants/... for tenants; a tenant's platformOrgId is its organization.