The term open source software is used to refer to those categories of software or programs whose license do not impose much conditions.
Open source software, generally gives users freedom to run or use the software for any purpose, to study and modify the program, and to redistribute copies of either the original or modified program, without having to pay royalties to previous developers.
Free software means the software is freely accessible and can be freely used, changed, improved, copied and distributed by all who wish to do so. And no payments are needed to be made for free software.
A program is free software only if users have all of these freedoms given below:
Open source software can be freely used, in terms of making modifications, constructing business models around the software and so on, but it does not have to be free of charge.
In open source software, the company constructing the business models around open source software may receive payments concerning support, further development.
In open source software, the source code is freely available to the customer.
A software which is free as well as open belongs to category FOSS (Free and Open Source Software).