Upon further reflection, I agree with Nanren888. Expert: somebody with a lot of knowledge or skill in something. Specialist: somebody with a lot of knowledge or skill in a particular subset of a field of study. A specialist is always an expert, but an expert is not always a specialist. I should add that some professions tend to use one word over the other. There are medical specialists that specialize in a part of the body. An eye specialist, also known as an ophthalmologist, is an expert in anatomy, physiology and diseases of the eyeball. We would not refer to them as eye experts. There are experts in the history of a certain time period or country. An expert in American history specializes in the history of the United States. We would not refer to an American history expert as an American history specialist.

Don't you believe that I can call myself a specialist when I have wide knowledge in a specific area with less experience. However, to call myself an expert, I should have extensive knowledge and experience in a particular area. Specialist = wide knowledge + less experience Expert =extensive knowledge + extensive experience

E.g mission specialist Smith. He has a specialisation, for example, electronics.

Domain dependent. Sorry. No universal answer. . Expert means that you know something well, or are good at doing it. You may or may not be good at other things. Specialist, really means that you specialise in that thing. You may or may not be good at it. . But, you are right. They tend to be used to mean close to the same thing, A specialist is given the benefit of the doubt that he/she is also good at their specialisation. . When? You are a specialist, when you have specialised on a topic/skill ... YOu are an expert when you know more than a threshold amount about something, or demonstrate skill above some threshold. . I'm always a little sceptical of anyone who calls themselves an expert. It's too easy a term to use. . At school my maths book was called "Advanced maths". Early in university it was "intermediate" something. Later on it was "Elementary" something. It seems the more you know about many things, the more you know of what you should know but don't. My guess is that you are an expert when others call you that. Hope this helps in some way. :)