A OpenStack cloud system suppose to be used by multiple users. A role based access system has been adopted on OpenStack which control access to the shared resource. Roles control the action a user can take. You can say that each tenant is a individual resource container.
Let us understand this through an example. I have following tenant on my openstack
There are four tenant in my openstack. The tenant I should for administration of OpenStack is admin. But tenant is container not a user so , if I list user available in openstack
Here there are multiple users are available. What if I map admin tenant to admin user? Apparently admin user have required privileges assigned to admin tenant. A tenant may map to a customer, account, organization, or project. When we access execute command we define username, password and tenant as well
Tenants are also known as Projects. On web interface (Horizon) you can list Projects