The term Khālsā (Punjabi: ਖਾਲਸਾ, pronounced [kʰaːl(ə̆)saː]) refers to both a community that follows Sikhism as its religion, as well as a special group of initiated Sikhs. The Khalsa tradition was initiated in 1699 by the Tenth Guru of Sikhism, Guru Gobind Singh. Its formation was a key event in the history of Sikhism. The founding of Khalsa is celebrated by Sikhs during the festival of Vaisakhi.

Guru Gobind Singh started the Khalsa tradition after his father, Guru Tegh Bahadur, was beheaded during the rule of the Mughal Emperor Aurangzeb after the Hindu Brahmins requested for his help to save their religion. Guru Gobind Singh created and initiated the Khalsa as a warrior with a duty to protect the innocent from religious persecution. The founding of the Khalsa started a new phase in the Sikh tradition. It formulated an initiation ceremony (amrit sanskar, nectar ceremony) and rules of conduct for the Khalsa warriors. It created a new institution for the temporal leadership of the Sikhs, replacing the earlier Masand system. Additionally, the Khalsa provided a political and religious vision for the Sikh community.

Upon initiation, a male Sikh was given the title of Singh meaning "lion". Kaur was made the sole, compulsory identifier for female Sikhs in the twentieth century. The rules of life include a behavioural code called Rahit. Some rules are no tobacco, no intoxicants, no adultery, no Kutha meat, no modification of hair on the body, and a dress code (Five Ks).

While originally a distinct subset of Sikhs, today the dilineation between Khalsa Sikhs and the wider, mainstream Sikh community has become blurred and muddled, despite most Sikhs not being formally ordained into the Khalsa order as Amritdharis. Most Sikhs hold the Khalsa institution in high-regard as the ultimate stage of a Sikh that serious Sikhs should aspire to become.

The term khālsā, is derived from the Arabic word خالص k͟hālis which means "to be pure, to be clear, to be free from, to be sincere, to be true, to be straight, to be solid".

Sikhism emerged in the northwestern part of the Indian subcontinent (now parts of Pakistan and India). During the Mughal empire rule, according to professor Eleanor Nesbitt, Khalsa originally meant the land that was possessed directly by the emperor, which was different from jagir land granted to lords in exchange for a promise of loyalty and annual tribute to the emperor.

Prior to Guru Gobind Singh, the religious organization was organized through the masands or agents. The masands would collect revenue from rural regions for the Sikh cause, much like jagirs would for the Islamic emperor. The Khalsa, in Sikhism, came to mean pure loyalty to the Guru, and not to the intermediary masands who were increasingly becoming corrupt, states Nesbitt.

The word "Khalsa" as used by Sikhs first finds mentions in the hukamnamas issued during the guruship tenure of Guru Hargobind, where he references the congregation of the east as being the "Khalsa of the guru". A later hukamnama issued by Guru Tegh Bahadur refers to the local Sikh congregation of Pattan Farid as being 'Guru ji ka Khalsa' ("Khalsa of the guru"). In a hukamnama of Guru Gobind Singh dated to 25 April 1699, he refers to a congregation of local Sikhs of Bhai Gurdas Bhagte Phaphre village as 'sangat sahlang', with the 'sahlang' term being a different designation from that of a Khalsa. According to the Dabestan-e Mazaheb, the 'sahlang' term referred to person(s) initiated into the Sikh religion by a masand, who acted as representatives on behalf of the Sikh gurus. Such Sikhs were termed as meli or masandia, and were differentiated from Sikhs who had received their initiation rites directly from a Sikh guru, whom were termed as Khalsa. Whilst extant hukamnamas of Guru Gobind Singh from the period of 1699 to 1707 refer to local Sikh congregations or individual Sikhs as being the guru's Khalsa (often with the phrase 'Sarbat sangat mera Khalsa hai' meaning "the entire congregation is my Khalsa"), with the coming of the end of a personal guruship, Guru Gobind Singh would then issue a hukamnama to the Sikh congregation of Varanasi on 3 February 1708 that referred to them as being 'Waheguru ji ka Khalsa' ("Khalsa of Waheguru").