The subject matter expert, or SME, is typically the lead expert on a particular topic.
Although they know the ins and outs of the topic, they may not have the aptitude for training or instruction.
The relationship between the SME and instructor should be strong. Instructors need to know what questions to ask to obtain the most relevant information from the SMEs for success in the classroom. In essence, the instructor translates the technical language from the SME into a language that any student can comprehend.
Sometimes SME is pronounced Smee like s+me.
Related to: project management, learning & development, expert, domain expertise