MUDRA

A mudra is a symbolic hand gesture meant to aid in concentrating the mind.  It is found in Hinduism and Buddhism.

While some mudras involve the entire body, most are performed with the hands and fingers only. In Hinduism, they are employed statically in meditation and dynamically in classical dance.

Mudras are used in yoga practice.  A famous book published by the Bihar School of Yoga is called Asana, Pranayama, Mudra, Bandha.  Asana are body postures.  Pranayama are breathing exercises.  Mudra are, again, symbolic hand gestures.  Bandha are "body locks," i.e. the way a participant holds the body postures in place.

As for Buddhism, common mudras are:

The Abhaya mudra represents protection, peace, benevolence, and the dispelling of fear.

The Bhumisparsha Mudra calls upon the earth to witness Shakyamuni Buddha's enlightenment at Bodh Gaya. 

The Dharmacakra mudra represents a central moment in the life of Buddha when he preached his first sermon after his Enlightenment.  In general, only Gautama Buddha is shown making this mudra.  It signifies the turning of the wheel of the Dharma.

The Dhyana mudra is the gesture of meditation, of the concentration of the Good Law and the sangha, i.e. the monastic order of monks.

The Varada mudra signifies offering, welcome, charity, giving, compassion and sincerity.

The Vajra and Jnana mudras are gestures of knowledge.

The Vitarka mudra is the gesture of discussion and transmission of Buddhist teaching.

The Karana mudra is the mudra which expels demons and removes obstacles such as sickness or negative thoughts.

In Tibetan Buddhism, mudras are believed to establish actual contact with gods.   These mudras are directed to thirty-five or more Tantric deities, great and minor, and run in sequences which often require thirty to fifty hand patterns in each sequence.  They are believed to not only attract the presence of the benevolent powers but also to drive off the evil ones.