Free software is software which encompasses the freedom of the user to share, copy and modify the software. It is defined in opposition to ‘proprietary’ or ‘closed source’ software, which is licensed according to the exclusive right of the copyright holder usually in a much more restrictive fashion than with free software (such as imposing a charge on the licensee to use the software, withholding the source code, and prohibiting users from redistributing the software to others). Often proprietary software is not interoperable, and thus incompatible, with other software. Usually a user does not have to pay to access free software, whereas proprietary software will encompass a charge for the user. Although this is not necessarily the case, since what makes proprietary software proprietary is more the control that the copyright holder has over how the software is distributed, whereas with free software anyone with a copy can decide whether and how much to charge for a copy and related services – but then someone else with the same copy might decide to redistribute the same thing for free.