Wikipedia
This is the anniversary of a guru's birth or death; marked by the holding of a festival. A gurpurb in Sikh tradition is a celebration of an anniversary related to the lives of the Sikh gurus. Observance of these anniversaries is an important feature of the Sikh way of life.
There are indications in the old chronicles that the gurus who succeeded Guru Nanak celebrated his b.day. Such importance was attached to the anniversaries that dates of the deaths of the first four gurus were recorded on a leaf in the first recension of the Scripture prepared by the Fifth Guru, Guru Arjan. The term gurpurb first appeared in the time of the gurus. It is a compound of the word purb (or parva in Sanskrit), meaning a festival or celebration, with the word guru. It occurs in at least five places in the writings of Bhai Gurdas (1551–1636), written in the time of Guru Arjan.
Among the more important gurpurbs in the Nanakshahi calendar are the birth anniversaries of Guru Nanak and Guru Gobind Singh, the martyrdom days of Guru Arjan and Guru Tegh Bahadur, and of the installation of the Guru Granth Sahib in the Harimandar at Amritsar. Other important gurpurbs include Baisakhi, which commemorates the creation of the Khalsa Panth, and the martyrdom days of the young sons of Guru Gobind Singh.
Gurpurbs are a mixture of the religious and the festive, the devotional and the spectacular, the personal and the communal. Over the years a standardized pattern has evolved, but this pattern has no special sanctity, and local groups may invent their own variations. During these celebrations, the Guru Granth Sahib is read through, in private homes and in the gurdwaras, in a single continuous ceremony lasting 48 hours. This reading, called Akhand Path, must be without interruption; the relay of reciters who take turns at saying the Scripture ensures that no break occurs.
Special assemblies are held in gurdwaras and discourses given on the lives and teachings of the gurus. Sikhs march in processions through towns and cities chanting the holy hymns. Special langars, or community meals, are held for the participants. Partaking of a common meal on these occasions is reckoned an act of merit. Programmes include initiating those not already initiated into the order of the Khalsa in the manner in which Guru Gobind Singh had done in 1699. Sikh journals and newspapers bring out their special numbers to mark the event. Public functions are held, besides the more literary and academic ones in schools and colleges. Gurpurbs commemorating birth anniversaries may include illuminations in gurdwaras and in residential houses. Friends and families exchange greetings. Printed cards like those used to commemorate holidays in the West are also coming into vogue.
Sikh fervour for gurpurb celebration reached new heights during the tercentenary of Guru Gobind Singh’s birth in 1967. This event evoked widespread enthusiasm and initiated long-range academic and literary programmes. It also set a new trend and format. Many subsequent gurpurbs were celebrated with similar fervor, including the fifth centennial of Guru Nanak’s birth in 1969 and the first centenary of the birth of the Singh Sabha in 1973. There is no firm evidence that centennials before the 1967 gurpurb were similarly observed. Max Arthur Macauliffe, a prominent 19th-century Sikh scholar, proposed a special celebration in 1899 for the second centennial of the Khalsa's creation, but it did not receive much popular support.