Terminal is the good 'ol unix bash command line shell (a little trivia here: bash is an acroynm standing for Bourne Again Shell - bash is an enhanced version of the original unix bourne shell).
Happily, bash is also the standard shell for most Linux systems, and so if you can pick up a good command line shell reference for Linux, you will have what you need... more or less. Mac OS X's Terminal based bash is from the underlying FreeBSD unix system that beats in the heart of every Mac, and there are minor differences between Linux bash and FreeBSD bash, but they are quite small. Nonetheless, if you can find a FreeBSD bash reference guide you are REALLY on top of it.
However, any good Linux shell reference will do nicely. A particularly good one that I use, and which is fairly recent, is the book "A Practical Guide to LInux Commands, Editors and Shell Programming" by Mark G. Sobell. This is a weighty tome, but it covers it all. The command line interface is AMAZINGLY powerful - remember the unix community had many, many years to enhance this thing before those new fangled GUI's like Mac OS X came along!