We at IEEE Software and Systems technical committee are interested to hear your understanding of the term Software Intensive Systems, and some examples of that.
I think the IEEE1471-2000 spells it out correctly:
"A software-intensive system is any system where software contributes essential
influences to the design, construction, deployment, and evolution of the system
as a whole"
The key words are "software contribution" and "essential influence". Certainly, for systems like that it is critical to assure that the software controlling the system behavior is not a hastily put together spaghetti code but has appropriate structure and clearly defined architecture. Specifically, for large and complex systems (air traffic management, fly-by-wire flight control, weapon control, etc.) having properly engineered software meeting precisely defined design criteria is a must.
A software-intensive system is anysystem where software contributes essential. influences to the design, construction, deployment, and evolution of the system. as a whole