Setting a clip’s In and Out points is a process called marking. You define the first frame you want to include in a sequence by marking that frame as the clip’s In point. Then you define the last frame you want to include by marking it as the Out point. In a typical workflow, you mark In and Out points for a clip in the Source Monitor.
Adjusting a clip's In and Out points after it is already edited into a sequence is called trimming. Typically, you trim clips to adjust how they play back in a sequence. For example, as you view the edit, you want to cut to the incoming clip a little sooner than you originally planned while marking clips. To fix that problem, trim the clip using trimming tools in Premiere Pro.
You can trim clips by dragging the edge of a clip. A clip's "edge" is a clip’s In or Out point, or edit point. Several specialized tools and techniques allow you to trim an edit point. These tools and techniques allow you to trim more easily and accurately, reducing the number of steps involved and maintaining the integrity of the sequence.
You can perform trimming tasks to selected edit points of a clip, or selected edit points from multiple clips. There are new icons for the tools, and when selecting edits with trim tools, the edit point is highlighted with a color related to the trim you perform.
You can use keyboard shortcuts on selected edit points to trim clips in the timeline. Trimming in Premiere Pro has a keyboard driven workflow, as there are keyboard shortcuts for every trimming task. See Timeline trimming.
You can use Trim Mode to help you dynamically trim edit points using buttons, or keyboard shortcuts. You can use the J-K-L keys to dynamically trim clips. See Work in Trim Mode.