I am writing a fantasy novel and there are many elements that will need explaining, such as precious items, cities, creatures and certain terms.

A glossary won't suffice and I'm stuck as to what this "section" should be called and where it should be placed. I'm thinking it should be placed in  the back matter as people may read it first if it is included in the front matter, thus eliminating any "surprise".

What is it called and where is the best place for it?