An earthworm is a big worm, similar to worms. They eat dirt, sort of. They eat the crap in soil. No, really, they eat crap in soil, decaying plant parts, they also eat nematodes, fungi and other things they find.
Earthworms have both male and female sex organs. When two worms meet up, they line themselves up pointing in opposite directions, with their clitella next to each other. They wrap up on eachother with the rest of their bodies around each other and exchange sperm packets. Then they leave eachother and each worm uses the sperm packet from the other worm to fertilize its own eggs. The worm then secretes a membrane around its clitellum and stores the fertilized eggs inside of a special membrane. Then the worm wiggles out of the membrane and leaves it behind a kind of worm cocoon, which hardens up to protect the eggs inside. When conditions are right, the eggs hatch and you have little, tiny, white baby earthworms.
Earthworms are good for your garden because the poop a lot, plus they eat pest dirt or infected dirt and they love moist and good soil as much as they love to make it.
What is better? Worm or Earthworm? Choose what you like most!