Prolegomenon is a noun that refers to an introduction to a book. 

Coming from the 17th century, our word of the day combines the Latin prefix P-R-O which means ‘before’ and the Latin word legein (lay JEN) meaning ‘to read.’ Before you read the actual content of a book, you read its introduction, or its prolegomenon. 

I loved that book I recently read on the modern problem of short attention spans, but I had to skip past that prolegomenon. I guess my attention span was just too short to endure a long, boring introduction.