Bindu is the Chakobsa word for "muscle".
The word was typically used by the Bene Gesserit Sisterhood when referring to control of the muscles, and way in which muscles were used.
It was often used in conjunction with prana, which meant "nerve".
Thus, if someone was said to have "prana-bindu" training, it was meant to denote supreme control of nerve and muscles.
'Bindu' in sanskrit refers to a seed visualised in tantric meditation (both hindu and buddhist).