Basic Zombie are the basic "zombie" unit; they are weak and easy to kill. In fact, it takes three shots for a Melon-pult to kill one of them. Having no special defensive equipment or travel abilities, these zombies are susceptible to any type of attack. They are found in almost every level. They are the first zombies the player encounters in every Plants vs. Zombies game. At the official start of a level, one will say "the zombies... are coming... brains..." and growl, signaling that the level has started. The Conehead Zombie and Buckethead Zombie become this zombie when their armor is destroyed.
Basic Zombie hates the term "Basic." He doesn't consider himself some generic foe or common corpse. He's an individual, darn it, and he's going to make a difference even if it kills you.