The phrase "golden mean" refers to finding a balance or middle ground between extremes. It suggests avoiding the extremes of excess or deficiency and instead seeking moderation and harmony. Full definition
A private Cloud, a sort of golden mean between those two extremes, lets you use your own infrastructure, on your own terms, either locally (in your datacenter) or externally (collocated, rented, etc.). (elearningindustry.com)
The polis as he described it was a kind of golden mean between the desolation of barbarism and the monstrous magnificence of empire. (firstthings.com)
Astronomers have discovered variable stars that periodically dim and brighten at frequencies close to the famed golden mean (scientificamerican.com)