One software license is required per developer.
Each license includes 1 Year Maintenance Subscription which can be renewed each year. The software is licensed perpetually however if you do not renew the maintenance then you will no longer be entitled to updates and priority support.

Standard License
Licensed to the company or organization. Each license can be used by one developer of the company. Perpetual license with annual maintenance renewal.

NetWork Named User License
With Networked Named User licensing, licenses are pre-assigned to specific users setup on the license server's user list. The Network Named User License is licensed to the company or organization. Each license can be used by one specific developer of the entity.

Concurrent License
With Concurrent licensing, users on different machines take turns using licenses from a shared pool. The Concurrent License is licensed to the company or organization.