Sources can come from many places. Here are just a few.
- Official records such as census records, vital records (birth, marriage, death), deeds, wills, military records, church and baptismal registers, etc.
- Photographs, videos and DVDs of individuals, places, or events
- Letters, e-mails
- Notes taken while interviewing someone
- Newspapers, magazines, journal articles
- Books and similar holdings of libraries, research centers, and museums
I deliberately didn't list the Internet as a source. The Internet is just a means of locating sources, like visiting a library, but is not a source in and of itself. That brings up another frequently used term, repository. The repository is the place where the source actually is maintained. I've found a family history book digitized online on the HeritageQuest web site. This book is also available through GoogleBooks and at several public libraries, all different repositories for the same source.
Genealogy.com's Genealogy Glossary defines source as "the document, record, publication, manuscript, etc. used to prove a fact". Attaching sources of information to our family history conveys that we are interested in recording facts, even if they aren't what we expected. Sources also help us and others distinguish facts from family lore or speculation.