On this wiki, especially on plant and zombie pages, normal damage shots (often shortened to NDS) are used to express the damage plants deal and the amount of health zombies have. Below is the explanation of such.
A bite from a zombie may be referred to as one normal damage shot, but this is disproved in ZomBotany and ZomBotany 2 where the pea shooting ZomBotany zombies do less damage with peas than with bites. However, this is proved when you hypnotize a zombie, because the bites from hypnotized zombies do the same amount of damage as a normal damage projectile, while normal bites do 1.55 damage. However, the previous sentence does not apply in Plants vs. Zombies 2, because a hypnotized zombie bite deals more damage than a normal zombie's bite due to the fact that a hypnotized zombie will always win between a battle with a zombie having the same exact health. Also, in the 5.7.1 update of Plants vs. Zombies 2, according to the data, normal bites have its damage lowered into 0.775, as well as divided all plants' toughness into half.
Some projectiles from plants can do more than just one NDS, and can do up to about four NDS, such as Cabbage-pult, Melon-pult, and peas ignited by a Torchwood. The projectile with the most damage output is Citron's charged plasma ball created during its Plant Food effect. It deals about 180 or less NDS of damage but is unknown why it stops immediately when it reaches a tombstone because other zombies tougher than a tombstone do not cause the plasma ball to stop.
Instant kills deal a heavy amount of damage, all will deal about 90 NDS, except for Primal Potato Mine, which deals 120 NDS. However, this may be disproved in ZomBotany 2 where a full-health Tall-nut Zombie can be exploded by a corn cob, Cherry Bomb, Jalapeno or Doom-shroom, even though it deals more damage than what instant kills usually deal with other zombies, so this may be a glitch. However, Potato Mines or Squashes cannot kill a full-health Tall-nut Zombie, despite having the same damage as the plants that cause explosions above. Chompers deal two NDS (ten in the sequel) to any zombie that it cannot devour.