Yeolmu or "young summer radish" is a type of Korean leafy radish. Crunchy and perfect for making yeolmu kimchi, a summery Korean dish. There's a reason that Yeolmu practically sounds like "yum" aloud.
Very nice radishes. However, I might note that I ordered "yeolmu" but got stuff with large taproots, that seems to correspond to what is advertised as "Korean radish" on the Weee! website; and the stuff certainly looks like "chonggak mu" (Ponytail radishes). The attached photo shows what I got. Perusal of the reviews for both items as offered by Weee! suggests that Weee! interchanges "yeolmu" and "chonggak mu" and/or "Korean radish" quite freely. So one may not get exactly what one ordered insofar as these radishes are concerned!