BibTeX is reference manager software most commonly used to work with references in LaTeX documents.  Rather than embedding individual references into the LaTeX document, BibTeX allows the user to pull references into the document from an external file dedicated to citation entries. 

Citations are stored in a .bib file (a plain text file) and can be easily edited.  Each entry begins with the reference type, @type, followed by the left curley brace ' { ' to indicate the beginning of the attributes for that entry, followed by a unique citation key used to identify that entry in the file, followed by the attributes of the item.  An example article entry appears below:

@article{fenn2006,
author="Fenn, J.",
title="Managing citations and your bibliography with bibtex",
journal="The PracTEX Journal",
volume="4",
year="2006",
}

Many databases, along with Google Scholar and citation manager programs like EndNote and Zotero, can produce references in the BibTex format.