Open-source software (OSS) is computer software that is available in source code form for which the source code and certain other rights normally reserved for copyright holders are provided under a software license that permits users to study, change, and improve the software.

Open-source software is defined by its licensing model, which grants users the rights to view, modify, and distribute the source code. This distinguishes OSS from proprietary software, where source code is kept confidential and modification rights are restricted. The definition accurately captures the essence of OSS licensing.