A phrase one often comes across in analytic philosophy of religion is "prima facie gratuitous evil". 'Prima facie', of course, means that we are going on first appearance, 'what things look like at first glance', as we often say. Sometimes instead of "prima facie gratuitous evil" we get "seemingly gratuitous evil"; I take these to be synonymous expressions. 'Gratuitous evil' is usually glossed, when people bother to gloss it at all, as something like 'evil such that even for God there is no adequate reason, based on what good can come from it or what bad can be avoided because of it, for permitting it'.
This is a rather bizarre notion. In talking about "prima facie gratuitous evil" we are talking about evil that appears to be what omniscient omnipotence could find no reason for permitting. How does something that's not intrinsically contradictory appear to be beyond the capacity of omniscient omnipotence to have a reason for? What does 'actual thing too irrational for omniscient omnipotence' actually look like? If we're talking about 'evil that appears to be gratuitous', how would one distinguish that in appearance from 'non-gratuitous evil that appears to require just more intelligence than any human being to have adequate reason for'?
The question here is not whether there is gratuitous evil or not, nor whether gratuitous evil is possible or not, nor whether we can establish that there is gratuitous evil or not. The question is this: What does it even mean in the first place for an evil to seem at first glance to be gratuitous? Perhaps someone somewhere does so, but I have never seen anyone justify describing any evil as appearing this way; the closest one gets is a few gestures that an evil is such that there is no obvious reason for it. But not immediately appearing to have a reason, or appearing in such a way that a reason is not obvious, is not appearing to be such that even omniscient omnipotence could have no reason for it. It is not even clear what the latter would mean.
It seems to me that the 'prima facie' is in this case sheer laziness. When we say that something is 'prima facie' X, this effectively sets the default to X; it can be presumed X unless there is some good reason not to do so. It makes one side of the argument easier. But if 'prima facie' is legitimately used here, there should be precise reasons, based on appearance alone, to take the evil to be apparently beyond the capacity of even omniscient omnipotence to find reason for rather than, say, apparently what nothing less than a being a hundred million tor a trillion times wiser and more powerful than any human being could find reason for. And there is nothing that I can think of that could possibly show up in mere appearance to a human being that would be able to distinguish them. One could perhaps distinguish them by very abstract and difficult metaphysical reasoning involving what is contradictory and what is not, but just prima facie? No. One might as well talk about the prima facie difference between the absolutely impossible and the humanly inconceivable; whatever difference there might be, it's not going to be discernible in the way things look like at first glance, but only at the end of a rather painstaking analysis.
Assuming that someone is not being merely lazy or deliberately trying to rig the argument, the only other cause I can see for this bizarre expression is a confusion between 'evidential' and 'prima facie'; and, indeed, one occasionally finds the 'evidential problem of evil' mischaracterized in terms of 'prima facie gratuitous evil'. But this is not a legitimate conflation; if there is any evidential problem of evil worth taking seriously, it is not going to be based on the 'prima facie' but on serious evidential analysis.