In Tantrism dhyāna comes to mean visualization of one's own deity (iṣṭadevatā), maṇḍala, centres (cakra) of the subtle body (liṅga/sūkṣma śarīra), or guru, accompanied by mantra repetition (japa) and symbolic hand gestures (mudra). Dhyāna as visualization is thus the visual equivalent of auditory mantra and corporeal mudra and is an essential part of sādhana.
"Dhyāna." The Concise Oxford Dictionary of World Religions. . Encyclopedia.com. (August 19, 2017). http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/dhyana
"Dhyāna." The Concise Oxford Dictionary of World Religions. . Retrieved August 19, 2017 from Encyclopedia.com: http://www.encyclopedia.com/religion/dictionaries-thesauruses-pictures-and-press-releases/dhyana