In a traditional book, the front matter is everything before the first chapter. This usually consists of a title page, a copyright page, and perhaps a table of contents, acknowledgements, and/or a preface.
In an eBook, the front matter can also include all of these things, but often doesn't. The title page and copyright page are usually included, but the table of contents, acknowledgements, and preface are often left out. This is because an eBook can have an interactive table of contents that is easy to naviagte, and because the acknowledgements and preface can often be found on the author's website or blog.