Stage 4 is not the same as terminal.
However stage 4 can sometimes be terminal depending on the condition.
Stage 4 such as in cancer, just indicates where the cancer has spread in the body (metastatic), and terminal indicates that the prognosis of the illness or cancer is not curable and eventually will result in death.
But stage 4 is not always terminal and many people with stage 4 illnesses like stage 4 cancer live for years.
But terminal illness or terminal cancer is what means that someone has a life expectancy of 6 months or less.
Stage 4 is just the measure of physical spread of the cancer.
It simply means that the cancer in stage 4 has spread from it's original site (primary tumor) to distant organs or tissues in the body.
While stage 4 cancer is often considered to be incurable, the main goal with treatment for stage 4 cancer is to extend life and manage symptoms like using systemic therapies such as targeted therapies, chemotherapy and immunotherapy and even palliative care.
The prognosis for people with stage 4 cancer drastically varies depending on the type of cancer.
Take for example stage 4 testicular cancer or even some types of lymphoma cancers are highly curable, although other cancers are treated as a long term, manageable illness.
Terminal is what refers to the cancer or illness that can't be cured and is expected to result in the persons death, often within 6 months or less.
When the cancer is deemed terminal treatment shifts away entirely from shrinking or controlling the tumor or cancer and solely focuses on end of life comfort and quality of life for the person.
The word terminal is usually designated when doctors determine that a persons life expectancy is limited, often 6 months or less.
Having a terminal diagnosis can also occur at earlier stages if the cancer is aggressive, but the word terminal is mostly frequently applied in advanced cases of cancer.