A complete set of products and services that are managed by an organization, representing its commitments and investments across all customers and market spaces. It includes the Service Pipeline (future), Service Catalog (live), and Retired Services (past).
Portfolio management ensures you aren't investing in "Zombie Services" that consume budget but deliver no value.
We use the 3 horizons model for portfolio management. Horizon 1 (Run/Optimize), Horizon 2 (Grow/Expand), Horizon 3 (Innovate/Explore). If 100% of your budget is in Horizon 1, you are dying.