When a character's gaze is directed to something off to their side. The most common instance is eyes looking 90 degrees across the shoulder, but may also include up to 45 degrees facing forwards or backwards, relative to the character's front, not the viewer's perspective. If the eyes are directed more than 45 degrees backwards use looking back instead.
If the character is also looking to the side without adjusting his/her head, use sideways glance too. Not to be confused with averting eyes, where a character is deliberately diverting their gaze from the viewer/other characters out of embarrassment, anger, annoyance, etc.
