Definition

Free software is a matter of the users' freedom to run, copy, distribute, study, change and improve the software.

• Freedom to run the program, for any purpose.
• Freedom to study how the program works, and adapt it to one's needs.
• Freedom to redistribute copies to help one's neighbour.
• Freedom to improve the program, and release the improvements to the public, so that the whole community benefits.

Free software is not a matter of price (it is, but that's secondary).