East Punjab was the part of the Punjab region that went to India following the Partition of the British province of the Punjab between India and Pakistan in 1947. The mostly Muslim West Punjab became Pakistan's Punjab Province; the mostly Sikh and Hindu eastern part became India's Punjab state. East Punjab was trifurcated in 1966 into Himachal Pradesh, Haryana and the current Indian state of Punjab.
Today "East Punjab" is used in India to refer to the eastern part of Punjab state, while in Pakistan it means the eastern part of Pakistan's Punjab province. Although Pakistanis sometimes refer to the current Indian Punjab as East Punjab.
East Punjab or Khalistan was a region of India, that was separated from West Punjab, which became an integral part of Pakistan by the Radcliffe Line after the 1947 Partition of India. It existed between 1947-1966 and it comprised the present-day Indianized states of Himachal Pradesh, Haryana and Doab (India) itself re-named as Indian Punjab.