Why Does My Screen Have a Dark Spot or Patch?

A dark spot isn't always a dead pixel. Identifying the type points you to the fix.

Possible causes

Pressure mark / "LCD bruise": a darker blotch from physical pressure (a thumb on the lid, an object in a bag). On LCD it may slowly fade; if the layer is damaged, it's permanent.
Trapped dust: a small dark fleck under the glass that doesn't change with color. Confirm with a White Screen.
Dead pixel cluster: several failed pixels close together — fixed dark on every color (Dead Pixel Test).
Backlight/diffuser damage: a shadowed region from a damaged backlight layer (LCD).

Cycle solid colors with the Color Test. A spot dark on every color = pixels/physical. A spot that varies = something else.
Check if it moves or fades over days (pressure marks sometimes do).

For fresh pressure marks: leave it, avoid more pressure — some recover.
Never press hard to "fix" it; you risk spreading the damage.
Physical damage to the panel or backlight generally requires a screen replacement.