Nyepi is a "Day of Silence" carried out by the Hindu people in the Island of Bali to commemorate every Saka New Year which this year is on 5 March. It is a Day of Silence, Fasting and Meditation from 6 a.m that day until 6 a.m the following morning.
Nyepi is reserved for self-reflection and as such, anything that might interfere with that purpose is prohibited. The main prohibitions are: no lighting fires (and lights must be kept low); no working; no entertainment or pleasure; no traveling; and for some, no talking or eating at all. The effect of these prohibitions is that Bali’s usually bustling streets and roads are empty, there is little or no noise from TVs and radios, and few signs of activity are seen even inside homes. The only people to be seen outdoors are the Pecalang, traditional security men who patrol the streets to ensure the prohibitions are being followed.
Although Nyepi is a Hindu holiday, but non-Hindu residents of Bali followed the Day of Silence as well, to respect for their fellow citizens. Even tourists are not exempted; although free to do as they wish inside their hotels, no one is allowed onto the beaches or streets, and the only airport in Bali remains closed for the entire day. The only exceptions granted are for emergency vehicles carrying those with life-threatening conditions and women about to give birth.
One day after Nyepi, known as Ngembak Geni, social activity picks up again quickly, as families and friends gather to ask forgiveness from one another, and to perform certain religious rituals together.
Source : Wikipedia.