# Glossary: Understanding pediatric rare disease clinical trials

This glossary explains some of the words you may hear if your child is involved in rare disease research or a clinical trial. It is designed to make medical and research language easier to understand, helping families follow what doctors, nurses, researchers, and study staff are saying. While created primarily for families, it may also be useful for others in the rare disease community, including health professionals, educators, and advocates.

This glossary was developed in Canada, and some terms reflect the Canadian healthcare and research context. Words, organizations, processes, or requirements may be different in other countries or regions.

The language used in the rare disease community continues to evolve. As research advances, treatments emerge, and families and advocates share their perspectives, the meanings of terms may shift. This glossary is meant to be a supportive tool to promote understanding.

In Canada, there is no single official definition of a rare disease. For the purposes of this glossary, we are using a commonly accepted working definition: a condition that affects fewer than 1 in 2,000 people. Many rare diseases start in childhood and are caused by changes in genes. While each rare disease might impact a smaller number of individuals, together they affect many families across the country and beyond.

Can’t find a word? 
We welcome your feedback and continue to update this. Feel free to reach out to by emailing us to: rkengage@mcmaster.ca

Authors
RareKids-CAN Knowledge Synthesis and Mobilization committee

Page last reviewed: 01-Oct-2026

Links

Glossary (PDF)