Data row = that which is found in a table (heap or clustered index)
Index row = that which is found in nonclustered indexes.
There are some differences in their details, but that's not important.
You say "Data row" and people will think you mean a row with all the columns that the table has. That is not what is in nonclustered indexes. They have just the index key, the pointer to the data row and any include columns.
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