When you hear people speak of "remission" they usually mean the absence of the original symptoms (shortness of breath, bruising, etc.), normal blood counts, and normal results for other tests. For MDS that would include normal results from a bone marrow biopsy, i.e., no abnormal morphology (cell shapes) and no bad cytogenetics (chromosomes). But sometimes they mean that these goals have almost been achieved.
It's clearer when they say "partial remission" if symptoms or signs of disease have mostly disappeared, but some remain, and when they say "complete remission" if there are absolutely no signs of the disease.
Medical researchers are more precise about their terms. In a research paper they will normal define "remission" in terms of specific ranges of numbers for specific tests.