Crushed Blacks
Shadow areas pushed to pure black so that separation between dark tones is lost.
In depth
Crushing can be a deliberate stylistic choice — it adds contrast and drama, and it hides noise — or an accident of underexposure and heavy contrast curves. The difference is intent and control: a deliberately crushed black usually sits behind a subject that still holds detail, while an accidental one swallows the subject itself.
Examples in practice
A low-key studio portrait crushes the background to true black on purpose; the same file crushed across the model's dark jacket loses the fabric's weave.