Punctum
Roland Barthes's term for the detail in a photograph that pierces the individual viewer and gives it personal force.
In depth
The punctum is accidental and unshareable — a particular pair of shoes, a broken fingernail — and it cannot be designed by the photographer, which is precisely Barthes's point. It names the experience of being unexpectedly affected by a picture whose subject one has no connection to.
Examples in practice
A viewer is arrested by a subject's worn wristwatch, a detail the photographer never noticed.