Nyasa (English: placing) is a concept in Hinduism. It involves touching various parts of the body while chanting specific portions of a mantra. This is considered to be invoking presence of the deity, of the mantra, inside the body.
Each mantra is associated with a specific Nyasa. There are various types of Nyasas, the most important of them being Kara Nyasa and Anga Nyasa.
Srividya followers practise Matruka Nyasa.
References
Nyasa (ritual) Wikipedia(Text) CC BY-SA