Rye flour refers to a type of flour made from ground rye grains. It is different from regular wheat flour and used in baking to make bread and other baked goods.
I mix a couple tablespoons of rye flour with enough water to make a paste. (thecrunchymoose.com)
To emphasize this point one more time, you will get your best results from making your sourdough starter with rye flour instead of wheat. (thehealthyhomeeconomist.com)
A general rule for using rye flour in everyday baking is to swap out one - third of the called - for flour with rye. (tastingtable.com)