MR – Manual Release
When a recipe indicates to do a manual release of pressure you are to release the pressure at the indicated time which is usually at the end of the cooking cycle. The method of releasing the pressure varies depending on your machine.
NPR – Natural Pressure Release
This indicates you are to let your pot turn itself off at the end of the cooking cycle and cool-down on its own. Do not touch the pressure release mechanism until the time indicated in the recipe for NPR has elapsed.
Sous Vide
This is a fancy name for what basically amounts to…. boil in bag. This is a function available on the Ultra models of Instant Pots.