An object close to the camera, or another person's shoulder, is shot blurred across the edge of the frame. It adds depth and gives a feeling of peeking in or of the other person being right beside you. A shot that focuses on one character with a bit of the other's shoulder in frame is called a "dirty single."
Over-the-shoulder shots in dialogue scenes, peeking shots through leaves, glass, or shelves, and ad shots with a blurry prop across the front of a product. Surrounding the subject with a door or window is a frame within a frame; foreground framing only covers part of the edge.
Static medium shot over the blurred shoulder of a man in a navy coat in the left foreground, framing a woman laughing across a small café table in sharp focus, an out-of-focus coffee cup and window reflections along the bottom edge, dirty frame, shallow depth of field, locked-off camera.
dirty frame, blurred shoulder in the left foreground, subject in sharp focus behind
OpenAI Sora 2 prompt guide (example prompt that specifies the foreground)