Perfect imbalance
Also said as Rotating meta, Controlled imbalance
Keeping a competitive game a little off balance on purpose, and changing which way it leans every so often. Players never settle on one solved answer, so there is always something new to work out. Extra Credits popularised the phrase in 2012.
A game in perfect balance can still go stale, once everyone knows the answer. Moving things regularly keeps old strategies from solidifying and gives people a reason to come back, as long as each change is small and nothing is left unplayable.
Say it
“Win rates are within 2% of each other, and nobody talks about the game any more. Pick a neglected champion every patch and nudge it up, so that the top three keep changing.”
Where you’ve seen it
League of Legends ships balance patches about every two weeks, so the strongest champions keep changing and players keep having to solve the game again.
Not to be confused with unbalanced
An unbalanced game has one answer and stays that way until someone fixes it. Perfect imbalance leaves many strategies close together, and moves the top spot on purpose.