Ekadashi is the eleventh tithi of each paksha, so it arrives about twice a month. It is especially associated with Vishnu.
Many observe it with a fast from grains and beans, spending the day in prayer, chanting or reading. The fast is broken the next day, during Dwadashi, at a time called parana.
Each Ekadashi of the year has its own name, such as Parivartini, Indira or Prabodhini, and its own story in the Puranas.
The exact observance date can differ between traditions, notably between Smarta and Vaishnava calendars.
