Abbreviated to NNT or NNTT, this is a simple statistical concept, relevant to clinical practice in medicine. It is the number of people you need to treat in order to gain some specified benefit. This number is quoted with reference to who you're treating, what the treatment is, the outcome of interest, and a time scale. Examples of commonly quoted NNT's are:

This number is good for working out whether it's worth trying some treatment, it helps you and your doctor do a cost/benefit analysis.