Solutions in a Lean environment tend to be temporary. The rationale behind the statement lies in the term continuous improvement. Any new process you develop, by definition, will eventually change. “Solution” implies that a problem is solved once and for all. The two terms don’t play nice together.
I don’t recommend that you become a stickler and ban the use of the term “solution” within your continuous improvement culture. I do, however, advocate that you make sure to realize that any process you have, no matter how good it seems today, will eventually become outdated and need to be changed.
In fact, the change may not even be driven by external forces. In many cases, as a team develops new skills and capabilities, it can approach a problem in different and innovative ways. If the previous change had really resulted in a true solution, that would not be the case.
The other challenge to using the term solution is that it implies there is a single right answer. The solution to 2+2 is always 4. The solution to “What size should this kanban be?” might have a variety of answers, depending on your requirements and assumptions.