I thought it is a common term by now but apparently it is not. Here is my definition of “write-only (research) journal”:

A write-only research journal is a research journal that publishes papers but is never read (hence write/publish-only). Its purpose is twofold: to (a) give a researcher some reputation return on their work by having it pass (some form of) peer review and to (b) make money for publishers.

David Rosenthal explains the economics of write-only journals. Basically, by increasing the mass of their offering through easily produced write-only journals, publishers appear bigger in bundling deals with libraries and can charge more for the access to their overall offering. Rosenthal then goes on to discuss other problems with peer review, the academic system, etc. but these are other topics.

Obviously, “write-only journal” is a derogatory term. Good research should be published in outlets that are read, not just written to. However, with the abundance of research results, I think even write-only journals serve the small purpose of validating the research results and hence the work of the researcher. However, the implication of write-only is that the results are not worth much and hence that validation should not count as much either. Which is why some say these journals should be done away with anyway.