GPL / LGPL - GNU General Public License/Lesser General Public License
The full license text can be found at http://www.gnu.org/copyleft/gpl.html
The licenses under which the Linux kernel and much of the utility and
library code necessary to build a complete system may be copied, distributed
and modified. Each portion of the software is copyright by its respected copyright
holder, and you must comply with the terms of the license in order to legally copy
(and hence use) it. One significant requirement is that you freely redistribute
any modifications you make; if you can't cope with this, embedded Linux isn't for you.