“Investments” in this context covers a very large array of possible actions that touch pretty much every single aspect of the business. Some examples include: large scale business projects (such as exploring a new market, or investing in a major new product development project), major transformation projects (such as digitization of a significant portion of the business), major financial decisions (such as share buyback programs) etc. SPM is conducted at the top executive level of the organization.
SPM has close ties to both PPM and Project Management, but at a much wider scope. SPM is becoming popular due to the need of more and more organizations to reinvent themselves in the face of disruptions such as the web or events such as the COVID pandemic.