It's All Greek to Me

A Prologue is a piece of writing at the beginning of a larger work, while an Epilogue is at the end. Now an Epigraph is a short saying or quote, again usually at the beginning of a larger work, while an Epigram is a short poem or saying with a twist at the end.
None of those should be confused with an Epitaph, which is text that honors the dead, and is usually on a tombstone.