Line Clear

Means the permission given from a block station to a block station in rear for a train to leave the latter and approach the former; or the permission obtained by a block station from a block station in advance for a train to leave the former and proceed towards the latter. (G.R. 1.02(36))

It is the permission given by the Station Master for a train to leave a station.

It is the permission given to the rear Station Master for train to leave that station and come to his station, or

It is the permission taken from the station in advance for train to leave his station and go to advance station.