Off-label use is when a drug is used for something other than for what it was approved.

A drug label describes the uses regulatory agencies have approved for the drug. 

The cost in terms of the value of the treatment compared to the best alternative option that was not chosen. For example, if the NHS decided to spend money on a new treatment for a rare disease, an opportunity cost would be that the money spent on this new treatment could not be spent on anything else.

Conditions that only affect a small group of patients. In the European Union (EU), the European Medicines Agency (EMA) defines this as a condition affecting fewer than 1 in 2,000 individuals (European Medicines Agency, 2015).

Another term for rare disease. They are conditions that only affect a small group of patients. In the European Union (EU), the European Medicines Agency (EMA) defines this as a condition affecting fewer than 1 in 2,000 individuals (European Medicines Agency, 2015)

A medicine developed for a rare disease.

Outcomes measures are measurements of the effects of a treatment or service. They might include physical measurements - for example measuring blood pressure - or psychological measurements - for example measuring people's sense of well-being. So if someone takes part in research, they may be asked questions or may be asked to have extra tests to assess how well the treatment or service has worked. 

A broad term often used to describe a variety of results from trials

A participant is someone who takes part in a research project. Sometimes participants are referred to as research "subjects".

This is a type of research where researchers and people who use services or carers are partners in a research project. The research addresses an issue of importance to service users or carers, who are involved in the design and conduct of the research, and the way the findings are made available. The aim of the research is to improve people's lives.

This is not a research method - it's an approach to research, a philosophy.