An organoid is a miniaturized and simplified version of an organ produced in vitro in three dimensions that shows realistic micro-anatomy. They are derived from stem cells (either pluripotent stem cells or adult stem cells) and can self-organize into structures that mimic the architecture and function of actual human organs.
The term was coined in the early 20th century, but the modern technology took off around 2010 when Hans Clevers' lab successfully grew intestinal organoids. Since then, brain, kidney, heart, and liver organoids have been developed.
Organoids are widely used in biological research for modeling diseases (including cancer and infectious diseases), drug screening, and personalized medicine. They offer a bridge between traditional 2D cell cultures and animal models, providing a more relevant human context.