Kalashtami or Kala Ashtami is a Hindu festival dedicated to Lord Kalbhairav and is observed every Hindu lunar month on the Krishna Paksha Ashtami Tithi (8th day during the waning phase of moon). The Ashtami Tithi after Purnima i.e. full moon is considered to be the most suitable day to worship Lord Kaal Bhairav.
Devotees observe this day in order to appease Lord Kaal Bhairav.
Cycle Pure wishes you a blessed Kalashtami.