Glossary:

Cold Process Soapmaking:  This method of soapmaking is cold process soapmaking.   There is also hot process soapmaking, rebatching, milled and transparent soapmaking, which is a variation of cold process soapmaking. 

Essential Oil:  This is the essence of the plant extracted in a distillation process.  Because it is a derivatives of the plant achieved without alcohol or chemicals, most essential oils will not seize your soap, though some, like cinnamon will cause reactions in some people.  If you would like to use essential oils, it may be a good idea to read some books on the subject, to ensure that you will not be using ones that are reactive.  Essential oils are considered to be a natural way to scent your soap with out the use of chemicals.  Unfortunately there are limitations to the variations that you can get, and they are very expensive.  As for the goodness that essential oils give to us, it is uncertain how many survive the lye bath.

Fragrance Oil:   The fragrance oils that you want to use should have been tested in Cold Process Soapmaking, and are skin safe.  It is possible to use oils that have not been tested for soap, but the chemical reaction of making soap is so precarious that a fragrance oil can make your soap into a scary thing.  I think that one of the terms used for the effect is mutating. 

Gel:  This is a stage that the soap goes through after it has been poured into the mold.  The soap in the center of your mold becomes dark and gel like, if you touched it you would see that it is in fact gel.  It is not necessary for your soap to go through gel, but in happens frequently.  The gel stage is a product of the chemical reaction between the oils and lye. 

Lye: Sodium Hydroxide or caustic soda

Saponification:  This is the chemical reaction between Lye and Oils

Sap Value:  This is the number that is used to calculate Potassium Hydroxide needed to make soap of the different oils.  Each oil has its own sap value.  Potassium Hydroxide is used to make soft soap.  To make a hard soap we use Sodium Hydroxide, and the numbers we give are used to calculate the oils to make a hard bar of soap, but these are not true sap values. 

Seizing:  This happens when something in your recipe has gone horribly wrong, and your trace happens so fast that if you can somehow glop the soap into your mold, you will have to press it into your mold.  This effect is also called soap on a stick. (thanks for the technical terminology Rachael)

Trace:  This is the stage in the process of soapmaking when the soap looks like a thick custard.  Your soap can go from trace to solid in about 30 seconds after a good trace has been achieved.  I like to add my herbs and fragrances at a very light trace, so I have plenty of time to pour. 

Resources:

If you need to know more information, or are addicted to soapmaking, this is the site for you.  Kathy Miller has been making soap for a long time and she goes into much more depth that I have.  Her site is considered THE place to start on your path to soapmaking.
www.millersoap.com

This is the address of a lye calculator, a must have if you want to calculate your own recipes www.thesage.com 

This site also has a message board called "The Soapmaking Exchange" where soapmakers go to ask and answer questions.  You will find a lot of other soapmakers ready and willing to help you if you get into trouble.   www.soapmaking/soapmak.htm

Books
Each of these books are a good resource, they each have their own methods and ideas, but they can each give you some bit of advice to help you understand soapmaking.

-The soapmakers companion by  Susan Miller Cavitch

-Transparent Soapmaking by Catherine Failer

- Soapmaking by Ann Bramson

- The Art of Soapmaking by Merilyn Mohr