This is a frequently asked question in Scaled Agile interview questions.   Solution train constructs complex solutions with a Lean-Agile approach. It organizes and coordinates multiple Agile Release Trains into one. It guides the attention of hundreds or even thousands of entities toward attaining a common goal. This is planned for creating solutions on a large scale. A solution train starts like a conventional SAFe Program Increment Planning session. But instead of having Agile Teams that become a part of the Agile Release Train, there are Agile Release Trains that participate.  The vision and the backlog are aligned. The dates are decided for the cadence and the schedule to follow. The planning of the budget is done according to an Economic Framework. This framework consists of lean budgets, epic funding, decentralized planning, and job sequencing. The Economic Framework effectively arranges the team to complete its business objectives by considering the business constraints and staying within the set budget.  At the end of every iteration, there is a solution demo. It is a demonstration of what has been done to get feedback from the stakeholders or product owners. It is used to evaluate the integrated solution that has been created by the Agile Release Trains in the Solution Train. After every solution demo, there is an Inspect and Adapt session. Problems are identified and are used to improve in the next iteration.