Theresa Torres describes Opportunity solution trees as a visual way to think about working towards an outcome throughout a discovery process.
You start from an outcome you want to achieve, a problem you want to solve. For each outcomes there will be one or more opportunities, potential spaces to explore, these are broadly our ideas on how we would want to approach the problem. For each opportunity there would several solutions, these differ in how we exactly want to execute on the idea we identified. And finally for each solution there would be experiments that let us learn about the specific solution.
This also explains why just exploring one solution for a given opportunity, and one experiment usually doesn’t tell that much about the possibilities in an opportunity.
Outcome, opportunities, solutions, experiments can be laid out into a tree structure.