A tumour is a lump inside the body made of cells that have grown too much and too fast. Normal cells in your body grow, do their job, and stop when the body says stop. Tumour cells miss that signal and keep making more of themselves, so a mass builds up where there should not be one. It can be in almost any part of the body — the brain, the stomach, the skin, a bone. A tumour can be as small as a pea or big enough to press on other organs, which is often what makes a person notice it and go to the doctor. Here is the part students usually do not know: a tumour is not the same thing as cancer. Doctors talk about benign tumours and malignant tumours. A benign tumour grows in one place, does not spread to other parts of the body, and is often not dangerous — many people carry one for years. A malignant tumour is the cancerous kind: it can push into the tissue around it and travel to other places in the body. So when a doctor says "we found a tumour", that is not yet a cancer diagnosis; the next step is tests to find out which kind it is. This word is medical, and it stays medical — you meet it at the hospital, in news about someone's illness, in health articles. In everyday talk people are more likely to say lump, or say cancer directly, because tumour sounds clinical and frightening. Note the spelling: British English writes tumour, American English writes tumor. Both are correct in their own place, and Taiwanese textbooks usually follow the American spelling. The adjective is tumorous, but it is rare; people say "a tumour" far more often than they describe anything as tumorous.