Agree with Bijla, Sikh and Khalsa are the same. To become a Sikh of Guru Nanak Dev Ji Maharaj , to Guru Tegh Bahadur Ji Maharaj, you took Amrit from Charan paul, that was how you were initiated into Sikhi, Guru Gobind Singh Ji Maharaj gave us Khande Bate da paul, by which we initiate in.
Differing ways same result, you become a SIkh of he Guru, and to become it, you ask for admission in, the admission in, is Amrit