Cancer staging is a process used by doctors to describe the severity of cancer in a patient's body. The stage of cancer is usually determined by three main factors: the size of the tumor, whether the cancer has spread to nearby tissues, and whether it has spread to other parts of the body. Here's a brief overview of the stages:

1. Stage 0: This stage is also known as carcinoma in situ. The cancer cells are only in the layer of cells where they began and have not spread to nearby tissues.
2. Stage I (1): This is an early stage of cancer, where the tumor is small and has not grown deeply into nearby tissues. It also has not spread to the lymph nodes or other parts of the body.
3. Stage II (2) and III (3): These stages indicate larger cancers or tumors that have grown more deeply into nearby tissue. They may have also spread to lymph nodes but not to other parts of the body.
4. Stage IV (4): This stage means the cancer has spread to other organs or parts of the body. It is also known as advanced or metastatic cancer.

The specific criteria for each stage can vary depending on the type of cancer. Staging is important for determining the most effective treatment plan and understanding the prognosis. Treatment options may include surgery, radiation therapy, chemotherapy, targeted therapy, or a combination of these. The stage of cancer at diagnosis is a key factor in deciding the best approach.