It's a versatile term that can refer to flour made from various grains, including:
* கோதுமை மாவு (kodhumai maavu): Wheat flour
* அரிசி மாவு (arisi maavu): Rice flour
* சோள மாவு (sola maavu): Corn flour
* பருப்பு மாவு (paruppu maavu): Lentil flour
So, when you are talking about ground flour in Tamil, simply use "maavu" and specify the type of grain if necessary.