The Khalsa is the order of initiated Sikhs founded by Guru Gobind Singh at Anandpur in 1699, and its creation reshaped the community from a following gathered around a living teacher into a self-governing body.
The founding at Vaisakhi
At the spring festival of 1699 the Guru called for those willing to give their heads, initiated the five who came forward without regard to their caste, and then had them initiate him in turn, so that the initiator and the initiated were made equal. The initiated took the name Singh, the women Kaur, undertook to keep the five articles of faith and a code of conduct, and were bound into a single disciplined order. The reversal by which the Guru received initiation from his own disciples is the founding statement of the order self-understanding.
A Guru that does not die
The Khalsa matters because of what it made possible when the line of human Gurus ended. Guru Gobind Singh declared that after him the Guruship would rest in the scripture, the Guru Granth Sahib, and in the community of the initiated, the Guru Panth, so that authority passed to a book and a people rather than to a successor. The Khalsa is therefore not one institution among others but the vessel into which the living authority of the Gurus was transferred, and its collective decisions carry the weight the tradition once gave to the Guru in person.