What is subject matter experts?

In the paper:
How to create a bullet proof URS
http://www.askaboutvalidation.com/featured_articles_expanded.php?uid=33

I red a term “subject matter experts”. The context is “The requirements should define clearly and precisely what the system should do and state any constraints. Requirements should be reviewed and approved by the stakeholders and the subject matter experts.”

I want to know what is subject matter experts. Is there a position or work function for this?
Thanks

Basically a SME is an individual who has in-dept knowlegde of the application/system/process etc that is being validated, it maybe an engineer that works with a particular piece of equipment day in day out that understands the system/process better than anyone else.

Hope that helps

Subject Matter Expert (SME) is a person who is an expert in a particular area. In software engineering environments, the term is used to describe professionals with expertise in the field of application but without technical project knowledge.

It also has a broader definition in engineering and high tech as one who has the greatest expertise in a technical topic. SME’s are often asked to review, improve and approve technical work, to guide others, and to teach.

Thats the defn. Yes if the the software being developed or validated is in a new area then yes SME s are hired as professionals to guide the QA and Valn team