LaTeX

LaTeX is used for math and scientific equations.  There is a lot of information about the TeX world, but Pressbooks will only use a small slice.  Sometimes an author’s book will be written completely in TeX and will need to be mostly converted to HTML.  Other times, the book will be written in Word, and the Word equations will need to be translated into TeX syntax.

It is important to recognize the limitations of LaTeX on Pressbooks.  Cross-referencing and indexing can be a big, if not impossible hurdle.  If an already-written book contains a large number of cross-references and index entries, it is probably more wise to keep it in TeX and only use a PDF version.

Wikipedia has a nicely condensed description of LaTeX.