Each vertical line drawn through the scene represents a single take from the moment the director says "Action" to the moment the director says "Cut." Each scene might require several camera angles and positions, with one or more takes, all of which are lined and identified alphanumerically.
The following is a brief summary of the lining techniques and numbering system shown in the example in
Lined Script Basics:
When the scene is recorded on videotape — in a sitcom shoot, for example — the lined script can also include timecode notes written next to specific lines of dialog that represent a sync point between the dialog on the page and the recorded dialog on tape. These sync points provide assistant editors or chief editors with a quick path to specific points in the source material.