marker
A visual reference point in the Timeline that identifies a specific frame. You can use markers to align different objects at specific points in time, quickly navigate to specific points in a sequence, add notes about a specific area in your project, and more. There are several kinds of markers:
Project markers are fixed to a specific frame or timecode value in the Timeline ruler.
Object markers are attached to an object (or clip) in the Timeline.
Template markers control the timing of templates that you export to Final Cut Pro.