Mudra
mudrāThe "seals": hand positions in a modern class, and a larger family of practices in the old manuals. Related: the bandhas, or locks.
In the Hatha Yoga Pradipika, mudras are serious machinery, taught for one explicit purpose:
In order, therefore, to awaken this goddess, who is sleeping at the entrance of Brahma Dwâra (the great door), mudrâs should be practised well.
The original Sanskrit
tasmāt sarva-prayatnena prabodhayitum īśvarīm / brahma-dvāra-mukhe suptāṃ mudrābhyāsaṃ samācaret
To awaken the sleeping power at the base of the body. The familiar hand gestures of a modern class are the gentlest members of a family that includes the internal locks (bandhas) a teacher means by "root lock" or "mula bandha."