ANSWER

SAFe, Scaled Agile Framework, is a collection of best practices and proven success patterns for defining and implementing agile software development processes at enterprise scale.  The creator of SAFe is Dean Leffingwell, who was also behind the Rational Unified Process (RUP).

SAFe helps manage the agile software product development process at the enterprise level by organizing the knowledge and best practices at four different levels which build upon each other:

• Portfolio Level
• Value Stream Level
• Program Level
• Team Level

In the language of the Scaled Agile Framework, there are 2 variants to consider in a given organization's quest of implementing an agile framework:

• 4-Level SAFe - Includes all of the four levels above and is suitable for very large solutions with hundreds of team members per value stream.
• 3-Level SAFe - Does not include the Value Stream level (as it assumes only one value stream) - it is mostly suitable for smaller teams and programs of 100 people or less.

Here's the big picture view of the Scaled Agile Framework (SAFe), including all four level:

The SAFe Portfolio Level provides the tools, roles, and techniques used to organize an enterprise around the agile principles.  This level includes the governance, budgeting, and the management of value stream in order to meet the organization's strategic objectives.  At the portfolio level, the enterprise strategy is represented by the Portfolio Backlog containing Business Epics.

The SAFe Value Stream Level was designed to be used by very large organizations which multiple and complex value streams.  This level allows strategic goals of disparate parts of the organizations to be deal with independently while, at the same time, allowing for the management of  complex inter-dependencies and constraints.  At the value stream level, the upcoming prioritized work is represented by the Value Stream Backlog containing Capabilities.

The SAFe Program Level is where value is delivered in support of the larger enterprise strategic objectives.  This is the level where the product development is coordinated among various Agile Release Trains (ART) concept of continuously delivering value as part of a given program initiative.  At the program level, the upcoming prioritized work is represented by the Program Backlog containing the prioritized Features.

The SAFe Team Level is where the agile development take place using agile teams of practitioners use ScrumXP, Team Kanban, or other agile methodology to delivery value at a set cadence via iterations (typically every 2 weeks).  As is common with most agile practices, the team level's prioritized work is captured in the form of a Team Backlog containing prioritized User Stories.