Secondly: Definitions of Safa and Marwah
Linguistically: Safa means “boulders”, or large, arid, barren rocks. Some hold that it means a smooth boulder.
Technically: Safa is a raised part of the hill of Abu Qubays. From it, sa`y begins. It is at the south end of the walking area.
Linguistically: Marwah are white, gleaming rocks. The plural is marw.
Technically: Marwah is a hill in Mecca. Sa`y ends at it. It is a part of the mountain of Qu`ayqi`an, which occurs at the north end of the walking area.

Thirdly: Definition of walking between Safa and Marwah
Technically: It means walking between Safa and Marwah traversing the distance between Safa and Marwah seven times during Hajj or `umrah.