Parasitoids are bugs that lay their eggs inside other bugs, and those eggs hatch into baby bugs that eat the insides of the host bug to survive. It's like the movie Inception, but for bugs!
Let's say there's a ladybug who has a caterpillar friend. A parasitoid wasp may come along and lay its eggs inside the caterpillar. Once the eggs hatch, the baby wasps will eat the caterpillar from the inside out, killing it.
It's not very nice, but it's how some bugs survive in the wild. Just like how lions eat other animals to survive, parasitoids rely on other bugs to provide food for their babies.