You may also have heard it called a “character shield” or sometimes “plot shield.” The informal definition of plot armor is a character's unusual or unbelievable abilities to survive physical damage/injury due to their importance to the story.

What is plot armor in anime?

Sometimes referred to as "Script Immunity" or a "Character Shield", Plot Armor is when a main character's life and health are safeguarded by the fact that he's the one person who can't be removed from the story.

What is an example of plot armor?

For examples where important characters are just magnitudes stronger than the poor slobs who can't take even one hit, see Almost-Lethal Weapons. Contrasts with Anyone Can Die, Plotline Death, Red Shirt (which is someone wearing a plot target).