Having reached problem-solution fit means that you’ve understood your customers’ needs/ jobs-to-be-done and their desired outcomes. It also means that you’ve created a solution that addressed these needs in a unique way, as customer feedback suggests so (validation of desirability). However, contrary to widely-held opinion it does not mean that you already have evidence that they would really buy it. This next inflection point in lean validation is called product-market fit.
/ˈprɑː.bləm səˈluː.ʃən fɪt/