It's what programmers make, and what software is made out of. It is writen in many languages; C++, Basic, java, perl, python, Ruby, php, shell scripting to name a few.
Code is the currency of the Free Software movement.
Like the works of any author, code is automatically copywritten, and the creator has the right to allow, or dis-allow use of the material, by attaching restrictions and/or terms of use. Open Source refers to a license that grants almost unlimited use; to copy, use, modify, sell and distribute. What's the catch ? To comply with the most common open source licensing terms (GPL) you can do anyhing you like with the material, but if you change it, and then re-distribute it, you must make your source code freely available, for others to copy, modify, sell, whatever, under the same terms.
