Most open source software does not cost money to use. Some programs charge subscriptions for support, documentation, or premium versions, but most are usable without paying a fee.

Open Source

Open source usually refers to software that is released with source code under a license that ensures that derivative works will also be available as source code, protects certain rights of the original authors, and prohibits restrictions on how the software can be used or who can use it.

For more information these on-line resources should prove useful:

Open Source Initiative (OSI): here
Open Source Initiative - business case: here
Wikipedia: here