Ekadasi (literally, "the eleventh day") refers to two days a month: the eleventh day after the new moon and the eleventh day after the full moon. Scriptures say that ekadasi is a most favorable time for increasing spiritual practices and minimizing bodily needs. Krishna devotees fast on these days in order to spend more time hearing and chanting about Krishna.
Traditionally, all Vaishnavas abstain from grains and beans on Ekadasi, taking only water, milk, or fruits. Many fast completely from all food and water. With the time saved by avoiding any elaborate cooking arrangements, some chant extra japa and/or spend more time reading Srimad-Bhagavatam or other scriptures. Some gather together and chant Krishna-kirtan all night or engage in extra Deity service.