Which type of software is freely available and can be viewed, edited, and customised by anyone because its source code is open to the public?

Introduction / Context:
Software can be distributed under different licences that define how users may use, copy, modify and share the program. One important movement in computing is the idea that users should be able to study the internal workings of a program and improve it. When developers publish the human readable source code and allow modification under an open licence, the software falls into a special category that has had a major impact on operating systems, web servers and many other tools. This question checks whether you recognise the standard term for software that is both freely available and customisable by anyone because its source code is open.

Given Data / Assumptions:

• The software is freely available to users.
• Its source code can be viewed and edited by anyone.
• Users are allowed to customise and redistribute modified versions subject to licence terms.
• The question asks for the correct descriptive label for such software.
• The options include several phrases using the word source.

Concept / Approach:
The globally recognised term for this type of software is open source software. Open source means that the original source code is made publicly accessible, and the licence allows users to study, change and share the code. Examples include the Linux kernel, the Apache web server and many programming languages. Free source, easy source and unpaid source are not standard terms in software licensing discussions. Some open source software is free of charge, but the key feature is openness of the code and the permission to modify it, not only zero price. Therefore, among the options, Open Source software is the correct and precise label.

Step-by-Step Solution:
Step 1: Focus on the key idea: the software can be edited and customised by anyone.Step 2: Recall that open source licences explicitly grant rights to view and modify the source code.Step 3: Identify the option that exactly uses the phrase Open Source, which is the standard industry term.Step 4: Observe that Free Source and Unpaid Source do not appear in common licensing discussions and are likely distractors.Step 5: Recognise that Easy Source does not describe licence freedoms at all.Step 6: Select Open Source software as the only accurate and widely accepted term.

Verification / Alternative check:
To verify this, think of well known communities such as the Open Source Initiative and projects hosted on platforms like GitHub that are labelled as open source. Their documentation emphasises that anyone can inspect and modify the code. They rarely use phrases like free source software. You can also recall that some open source software may be sold as part of support or service contracts, which shows that open source is not only about cost but also about freedom to study and change the program. This confirms that the right descriptive term is open source software.

Why Other Options Are Wrong:

• Free Source software is not a standard phrase; it confuses the idea of free of charge with the idea of free access to source code.
• Easy Source software suggests simplicity but does not imply openness or licensing rights.
• Unpaid Source software focuses on cost and ignores the essential features of openness and modifiability.
• Locked Source software is the opposite idea, referring to proprietary programs where the source code is hidden.

Common Pitfalls:
Many people confuse the words free and open. Some proprietary software can be free to download but still closed source, meaning the code cannot be modified. Conversely, some open source projects are sold as part of enterprise distributions even though their code remains open. Exam questions often test this distinction. To avoid mistakes, remember that open source emphasises access to source code and rights to modify it, while free software may refer simply to zero price. In this question, the ability to edit and customise clearly points to open source software.

Final Answer:
The correct answer is Open Source software, which is freely available and can be edited and customised by anyone because the source code is open.