Stem cells are a class of multipotent cells with the ability to self-renew. Under certain conditions, they can differentiate into various functional cells. Based on their developmental stage, stem cells are categorized into embryonic stem cells and adult stem cells. According to their developmental potential, they are divided into three types: totipotent stem cells (TSC), pluripotent stem cells, and unipotent stem cells (also known as specialized stem cells). Stem cells are undifferentiated and immature cells with the potential to regenerate various tissues, organs, and even the human body, earning them the name "universal cells" in the medical field.