NPR is short for natural-pressure-release. After pressure cooking in an Instant pot you do have two options to release the pressure. Option one is to release the pressure using the quick-release-valve, which will depressure the instant pot in about 30 seconds.
But some recipes require a NPR. In this case do not use the quick release. After the instant pot finished cooking, just let it sit without doing anything. After 10-20 min the pressure-pin will drop automatically. This extra cooking time is needed in recipes calling for a NPR.
NPR = Let pressure release naturally for specified time mentioned in the recipe, then, if safety pin hasn’t dropped on its own yet, release remaining pressure manually.