What is open source software?

by OSS Watch on 1 May 2005 , last updated 14 May 2012

Introduction

The definition of open source

For OSS Watch, open source software is software that has been released under an Open Source Initiative (OSI) certified licence. OSS Watch uses this OSI-approved list as a means of avoiding debates over interpretation of the open source definition and which licences do or do not conform to it. By recognising the OSI as the appropriate final authority in this issue, much confusion is avoided.

Each of the licences approved by the OSI meets the conditions of the Open Source Definition. That definition includes 10 criteria. Perhaps the most important of these are the free redistribution of the software, access to the source code, and the permission to allow modifications to the software and derived works that may be distributed under the same licensing conditions.

Very different styles of licence meet these criteria. The GNU General Public License, commonly known as the GPL, meets the criteria. The MIT licence, which is very different in length and intent from the GPL, also meets the criteria. Indeed, around 70 licences have gone through the approval process. To help with navigating through these licences OSS Watch has produced a series of documents that describe some of the key licences in plain English.

For an individual or project looking to license their code, using an OSI-approved licence can simplify the process. In fact, many people (including OSS Watch) do not consider software to be open source unless it is released under an OSI approved licence. For potential contributors and users who wish to work with open source, it provides a quick way to check that the code is indeed open and accepted by a large community.

Is open source ‘only’ a licence?

The expression open source has wide application. For the OSI it also refers to the distinctive software development methodology employed by many open source software projects. The OSI home page starts with ‘Open source is a development method for software that harnesses the power of distributed peer review and transparency of process.’ However, the OSI stops short of defining this methodology in the Open Source Definition, which concerns itself only with the requirements of a licence designed to protect this way of developing software.

The open development methodology is based on principles that may not be among the principles of software development normally taught in academia. Open source software, strictly speaking, may or may not be developed using an open development methodology. The choice of which development methodology to adopt is dependent upon a project’s chosen route to sustainability.

Does open source mean anything else?

The term ‘open source’ originated in the worlds of journalism and intelligence, and referred to a publicly available source of information. This former use was known to the founders of the Open Source Initiative, and was felt to be ‘a feature, not a bug.’

Sometimes open source is conflated with open content or free content. Open content refers to content that can be edited, changed and added to by any reader. A good example is the famous Wikipedia, an online open content encyclopaedia. Open source is used today in various contexts which take it far beyond its application in software. However, to re-state, for OSS Watch open source software always refers to software released under an OSI-certified licence.

Is open source software the same as ‘free software’?

Free software is an expression used by the Free Software Foundation. The term ‘free software’ pre-dates open source software, and focuses on several kinds of freedom that are associated with the software, thereby taking a more ethical viewpoint on the matter. For some, it is the preferable term and they do not wish to associate themselves with the term open source. Free software must not be confused with ‘freeware’, which is software that can be acquired at no cost but for which source code may well not be available.

When we at OSS Watch use the term open source software without a more specific qualification, this will usually include both Free and Open source software. A common abbreviation for this collection of software is FOSS.

OSS Watch provides unbiased advice and guidance on the use, development, and licensing of free software, open source software, and open source hardware.