In filmmaking, the term Tight On basically refers to the Tight Shot which is used to create a "close and crowded" of characters and/or object within the scope of the lens.
toc_collapse=0;Tight On is used as a camera direction to the Cinematographer. It may or may not appear in the shooting script and is up to the discretion of the director.
When appearing in a script, Tight On appears in the action line of a shooting script and acts intructions for the cameraman.
BARRY
You think I'm kidding?
Barry walks to the door then turns
Camera moves TIGHT ON Barry's face.
BARRY
Try me.