Simple Definition:

Metamorphosis is a process in which an organism undergoes a complete change in its body structure and appearance. This transformation occurs in stages, with the organism going through different developmental forms before reaching its final adult form.

For example, a butterfly undergoes metamorphosis, starting as an egg, then becoming a caterpillar, forming a chrysalis [the stage of development when it is covered by a hard case, before it becomes an adult insect with wings], and finally emerging as a fully developed butterfly.

Very Simple Definition:

Metamorphosis is when an animal changes its body and looks completely different as it grows. This happens in steps, like a butterfly turning from a caterpillar into a butterfly. It starts as an egg, becomes a caterpillar, then a pupa [a step where it’s inside a hard case], and finally becomes a butterfly.