So a week or so ago, I made the frw-universe tag; made a tag-wiki for it too. Recently, a certain someone (not relevant who) made it a synonym of cosmology. For the record, it is currently the only synonym of cosmology. I think this was not valid. I'd like to state my disagreement with this action and request that it be undone.
Cosmology is a broad field that applies to a very large number of topics. It is true that frw-universe would be a subset of cosmology, but it is not a synonym. frw-universe only applies to topics that include a scale factor, are about the GR model of the universe we live in, and make some reference to the slightly more advance concepts like Friedmann equations, Hubble radius, co-moving quantities, or the like. Whereas cosmology can be applied to a much broader range, such as AdS/CFT, Schwarzschild space, asymptotically de Sitter solutions, and many others.
You could have a question that asks about the problem with using de Sitter space as a model for the universe we live in. That would be tagged as cosmology, but it should not be frw-universe. Similarily, a question asking about cosmological redshift is a cosmology question and it is probably within an FRW-universe, but the question shouldn't be tagged as frw-universe any more than a question about radioisotope dating should be tagged with standard-model Additionally, a question that asks about finding the Ricci tensor for a higher-dimensional FRW metric could be tagged under frw-universe (albeit, it would be more appropriate as frw-metric, but those would more likely be synonyms) and general-relativity, but I wouldn't necessarily put it under cosmology.
Furthermore, if this is a simple case that 99% of the time when frw-universe is used, cosmology will also be used, then I'd like to point out the existence of dark-energy, space-expansion, big-bang, or possibly the worst for that particular crime: cosmological-inflation. These are all allowed and often used without being recast as synonyms.
Based on all this, I think the synonymizing should be reversed.