Font Definitions
Copyright
Unless you know otherwise, you should assume all fonts to be copyrighted works that are someone's property and treat them as you would any other software. Fonts are software products in their own right, and are protected by international copyright law as well as individual license agreements. Even redistributing so-called 'freeware' or 'public domain' fonts is problematic. If you have created a font yourself (without using anything from other fonts), it is your property.
The use of any commercial font is governed by the terms of its manufacturer's End User License Agreement (EULA). Several major font vendors specifically allow altering a font, as long as the altered font is only used on machines for which you have licensed the original font. If you have questions about what can or can't be done with a font, you should contact that font's manufacturer.
Most font designers will not allow you to sell their font for profit or to include it in another product or CD-ROM compilation without permission and in most cases you will not be allowed to use parts of the font to create your own font. Detailed copyright information is usually included in the included font zip-file as readme.txt, copyright.txt or an equivalent text file.
Shareware
Try before you buy -- shareware fonts can be downloaded and evaluated for free before buying them. Individual shareware licenses differ in detail -- some specify a maximum trial period, some request registration while others require it, some require registration only for commercial use and allow free non-commercial use of the font. Shareware fonts are copyrighted by their author, meaning that further restrictions usually apply to alteration, reproduction, publication and distribution of the font.
Freeware
Freeware fonts can be downloaded and used free of charge for both non-commercial and commercial use. Although these fonts are available for free, the author retains the copyright, meaning that restrictions usually apply to alteration, reproduction, publication and distribution of the font.
Demoware
Demoware fonts are trial versions of fonts. They often do not contain a complete set of characters or have unique symbols in place of key characters. Demoware is similar to the shareware concept in that you may evaluate the font and are then encouraged to buy the full font. Demoware fonts are copyrighted by their author, meaning that further restrictions usually apply to alteration, reproduction, publication and distribution of the font.