According to the ServiceNow documentation1, a program is a container for the following:

Program tasks: Tasks that define the scope and deliverables of the program2.

Issues: Problems that affect the program or its outcome3.

Cost plans: Plans that estimate the cost of the program and its components4.

A portfolio is not a part of a program, but rather a collection of programs and projects that are aligned with a strategic goal or objective.

1: https://docs.servicenow.com/bundle/vancouver-it-business-management/page/product/project-portfolio-management/concept/c_ProgramManagement.html 2: https://docs.servicenow.com/bundle/vancouver-it-business-management/page/product/project-portfolio-management/task/t_CreateAProgramTask.html 3: https://docs.servicenow.com/bundle/vancouver-it-business-management/page/product/project-portfolio-management/task/t_CreateAnIssue.html 4: https://docs.servicenow.com/bundle/vancouver-it-business-management/page/product/project-portfolio-management/task/t_CreateACostPlan.html : https://docs.servicenow.com/bundle/vancouver-it-business-management/page/product/project-portfolio-management/concept/c_PortfolioManagement.html