This is related to
What's special about "unity-gain stable"?
which is about unity gain stability.
But what exactly does it mean if some op-amp is said to be only stable to, say, gain 3 rather than all the way down to unity gain?
Guesses:
Does this gain 3 refer to open-loop gain? (The amplifier has an adequate phase margin at the upper frequency where open-loop gain is 3, but not beyond?)
Or does it refer to closed-loop gain? (The amplifier will be stable up to its unity open-loop gain frequency, if the closed-loop gain is not less than 3?)
Best Answer
To expand on my comment, they are talking about closed loop gain.
If an op-amp is not unity gain stable, it has to be stable under some conditions, or what's the use of it?
So, if they say the op-amp is "gain-of-3 stable", they're telling you, this op-amp is not unity gain stable, and the minimum gain where it is stable is 3.