SAFe presents a single, unified view of the work to executives, allowing them to drill down for details or up for trends and analysis
A team in SAFe might be 8 to ten people, with everything they need to deliver software, end-to-end: requirements, coding, testing and deployment. Several teams create what SAFe calls a release train, which organizes around a program (more on that below). That’s a single project, or at least, one program-of-projects. It has a single line item in a budget – the company is buying one specific thing. This is the “small project” the executive talks about.
A portfolio is a collection of these programs, the total amount of budget dollars within IT going into software development. SAFe calls this “Program Portfolio Management,” and suggests that one office have the responsibility for strategy and investment funding, program management and funding.
In SAFe terms, the “Release Train” is the team-of-teams, typically 50–125 individuals. Like a real train, the release train runs on a schedule, though that schedule can be as flexible as your organization needs it to be. This Program Increment (PI) is described in more detail below. SAFe suggests that people involved in a release train be dedicated full-time to that release train, regardless of reporting structure.

The Scaled Agile Framework, or SAFe, provides a recipe for adopting Agile at enterprise scale. It is illustrated in the big picture.
As Scrum is to the Agile team, SAFe is to the Agile enterprise.
SAFe tackles the tough issues – architecture, integration, funding, governance and roles at scale. It is field-tested and enterprise-friendly.
SAFe is the brainchild of Dean Leffingwell.
SAFe is based on Lean and Agile principles.
There are three levels in SAFe:
* Team
* Program
* Portfolio
SAFe defines an Agile Release Train (ART). As iteration is to team, train is to program.
The ART (or train) is the primary vehicle for value delivery at the program level. It delivers a value stream for the organization.
SAFe is three letter acronym (TLA) heaven – DBT, ART, RTE, PSI, NFR, RMT and I&A!
Between 5 and 10 teams work together on a train. They synchronize their release boundaries and their iteration boundaries.
Every 10 weeks (5 iterations) a train delivers a Potentially Shippable Increment (PSI). A demo and inspect and adapt sessions are held. Planning begins for the next PSI.
PSIs provide a steady cadence for the development cycle. They are separate from the concept of market releases, which can happen more or less frequently and on a different schedule.
New program level roles are defined
* System Team
* Product Manager
* System Architect
* Release Train Engineer (RTE)
* UX and Shared Resources (e.g., security, DBA)
* Release Management Team
In IT/PMI environments the Program Manager or Senior Project Manager might fill one of two roles. If they have deep domain expertise, they are likely to fill the Product Manager role. If they have strong people management skills and understand the logistics of release they often become the Release Train Engineer.
SAFe defines a Scaled Agilist (SA) certification program for executives, managers, architects and change agents responsible for leading SAFe implementations.

–Slimane Zouggari