While selling your images may be the dream of many photographers, dealing with confusing contracts isn't part of that dream. To understand photography licensing rights you must first understand that unless you are selling a print, you are not "selling a photo" as such. What you are doing is selling permission to use that photograph in a certain way for a certain length of time. This is called licensing. While there are some basic common terms relating to licensing, there are as many different licensing situations as there are photographs. Understanding those common terms will help you understand more complex and customized terms as you endeavor to license your images.
Commercial rights can be a very murky term when corporate lawyers get involved. However, a general explanation would be that commercial means any endeavor designed to create income or use by a commercial entity. Some examples would include a sales brochure, magazine, advertisement, or billboard. Any advertising or promotional use would require commercial rights.
Non-commercial rights would be items that are not designed to create significant income. It may be used by individuals or other non-corporate type groups. Things such as church bulletins or printing an image to put on a school binder would be non-commercial usage.
When the word "first" is placed in front of other rights it simply means that the entity purchasing these rights gets to publish/use the image before anyone else who has purchased license rights.
Serial rights apply to magazines. This means that the magazine is licensing the right to use the image in magazine format. In other words, if you sell serial rights to magazine A you can't sell licensing rights to magazine B as well (unless you only sell "first" rights—then you can sell more rights later).
Watch out for this clause. Non-exclusive rights can be a reasonable license to sell but they can also be a quick way to lose the use of your image. The term "non-exclusive rights" means that the licenser has a specific set of rights at the same time someone else has them as well. The problem is that this clause is usually followed by a large number of specific rights. Many companies use this type of clause to allow them to reprint and resell your work on their own.
One-Time Use Rights
One-time use rights, also called single-use rights, are very easy to manage. One-time use means that the entity buying the license can use your image "one time" for one specified project. You are not granting permission for them to use the image in any other project. The photo may be reproduced for a large run of a magazine, but only a single time.
Understanding Photography Rights
Use this general information as a starting point. If you are given a licensing agreement to sign, be sure to read it carefully. Ask questions about any parts that are unclear. You should always check with your lawyer for concrete answers to legal questions for your particular situation.