Open source

Computer software with its source code (human readable code) made available with a license in which the copyright holder provides the rights to study, change, and distribute the software to anyone and for any purpose. Open source software may: be developed in a collaborative public manner; be reviewed by multiple professional and amateur programmers; require a fee and be licensed like other software; be fully open source or may have only a portion of the software open source.

Source: Election Terminology Glossary - Draft, National Institute of Standards and Technology (NIST),