RMS has an article for differences between them.
Free software is a convenient and powerful way to use a computer, but it is more than that.
Free software is the the basis for a community of freedom that you can join. With free software, you have freedom to change software when you wish, as you wish. You can ask a friend to change it for you, or hire a company to change it for you. With free software, you have the freedom to share with your neighbors, and your neighbors have the freedom to share with you. This community of freedom is the reason that we founded the Free Software Movement.