Apple Final Cut Pro 6 - Manual (Page 581)

248 Part II Rough Editing
 In points: This option aligns all clips so the In point of each clip is synchronized. If you
use this method, you first need to visually identify a common sync point (such as a
clapboard closing) in each clip by setting an In point. If a clip has no In point set, the
Media Start is used.
 Out points: This option aligns all clips so the Out point of each clip is synchronized.
Before you use this method, you need to establish a common sync point by setting
an Out point in each clip. This method is useful if your footage has a tail slate (a
clapboard recorded after a scene ends). If a clip has no Out point set, the Media End
is used.
In point of each clip
Out point of each clip