A.12.5.1 concepts

Answer:

"... software on operational systems.", as part of the description of control A.12.5.1 (Installation of software on operational systems) of ISO 27001 Annex A, refers to any software that is used in normal daily operations of an organization. This includes either software used on datacenters (e.g., database management systems, corporate backup software, etc.), as well as software used on employees workstations (e.g., e-mail clients, word processors, etc.).

For examples of implementation to support this control I suggest these materials:
- How to set security requirements and test systems according to ISO 27001 https://advisera.com/27001academy/blog/2016/01/11/how-to-set-security-requirements-and-test-systems-according-to-iso-27001/
- How to manage technical vulnerabilities according to ISO 27001 control A.12.6.1 https://advisera.com/27001academy/blog/2015/10/12/how-to-manage-technical-vulnerabilities-according-to-iso-27001-control-a-12-6-1/
- Implementing restrictions on software installation using ISO 27001 control A.12.6.2 https://advisera.com/27001academy/blog/2016/02/08/implementing-restrictions-on-software-installation-using-iso-27001-control-a-12-6-2/