Directly translated as the Pure Ones.
However this word from Sikhism is used to refer to Sikhs who have undertaken the Sikh baptism known as Khande-da-Pahul(Baptism of the Sword). Upon recieving the baptism, the Khalsa Sikh is required to maintain the Panj Kakaars(or 5 K's) and abstain from the 4 Kurehats.
There has been recent debate that the Khalsa does not necessarilly mean only the pure ones who have partaked in the Khande-da-Pahul but is also meant to be a general reference to the good and holy people of all religions and races.