The organ usually meant by this question is the liver.
Why the liver
- The liver is the only internal (visceral) human organ with a strong, well-documented ability to regenerate lost tissue and restore its original mass after part of it is removed or damaged.
- As little as about one quarter of a liver can grow back to full size by the remaining cells enlarging and dividing, allowing the organ to regain normal function.
A note on “only”
- Other organs like the kidney, lungs, and pancreas can repair or compensate for damage to a limited extent, but they do not regrow large missing parts the way the liver does.
- For this reason, biology and medical textbooks commonly refer to the liver as the only human organ that can truly regenerate itself.
