What an eclipse is, in panchang terms. A solar eclipse (Surya Grahan) can only occur on Amavasya, when the Moon stands between the Earth and the Sun; a lunar eclipse (Chandra Grahan) only on Purnima, when the Earth stands between the two. The panchang treats a grahan as a precisely bounded window — first contact to last contact — computed astronomically. There is no ambiguity in the timing itself; every almanac agrees to the minute.
Sutak Kaal is the period before. Tradition marks an inauspicious span leading into the eclipse: reckoned as four prahars (about twelve hours) before a solar eclipse and three prahars (about nine hours) before a lunar one. During Sutak, custom holds that temples close their doors, new undertakings and cooked food are set aside, and routine puja pauses until the eclipse ends and spaces are cleansed. How strictly households observe this varies widely by region and family practice.