Like Free software licences, Free content licences can be copyleft (where distributing modified works is only allowed under the original, Free licence) or non-copyleft.
The Design Science License (DSL) and GNU Free Documentation License (GFDL) are examples of copyleft licenses for free content; the FreeBSD Documentation License is an example of a non-copyleft license. The GFDL is the being used for the text of Wikipedia.
Other examples of free content licenses are some of those published by Creative Commons, when commercial use is not restricted.
See also: public domain