There isn't one single biological name for millet because "millet" isn't a single species. It's a common name for several different grain crops from the grass family (Poaceae).

Here are the biological names for some of the most common millet species:

* Pearl millet: *Pennisetum glaucum*

* Foxtail millet: *Setaria italica*

* Finger millet: *Eleusine coracana*

* Proso millet: *Panicum miliaceum*

* Sorghum (also called great millet): *Sorghum bicolor*

* Barnyard millet: *Echinochloa frumentacea*

So, to be precise, you should use the specific biological name of the millet species you're referring to.