CMS stands for Content Management System. It is a type of application software or set of related programs that allow users to create, manage and modify digital content, usually for websites, without the need for specialized technical knowledge. CMS platforms provide an intuitive user interface in which users can easily add, edit and publish content, manage multimedia files and control various aspects of their website's design and functionality.

The primary purpose of content management systems is to manage information across websites and enterprise systems. Whether it is a personal blog or a corporate website, a content management system allows users with no knowledge of HTML and CSS to add content. Some of these systems provide only the functions necessary for the average user in an easy and accessible way, while others allow for extremely complex data manipulation. The system can also be used as a central repository containing documents, movies, photos, phone numbers, scientific data, etc. 

There are two main types of CMS:

Open-Source CMS: These are CMS platforms that are developed and maintained by a community of developers. Examples include WordPress, Joomla, Drupal, OpenCard, and others. An open source CMS is usually free to use and users cannot customize the code to fit all of their specific needs.

Custom CMS: A custom CMS is a content management system that is specifically built and tailored to the requirements of a particular website. Unlike an open source CMS, which has a standardized code base that serves a wide range of users, a custom CMS is created from scratch, with features and functionality designed to meet the specific needs of a single organization, company, or business.

Here are some of the benefits of a custom CMS that make it the better choice:

1. Flexibility and control: It can be modified and adapted to the client's needs without being constrained by existing frameworks or plugins. An open source CMS always has limitations in meeting specific personal requirements.

2. Security: Custom CMS systems can potentially offer better security precisely because the source code is unique, which makes it less susceptible to attacks directed at known vulnerabilities in popular open source CMSs.

3. Complexity and cost: Developing a custom CMS can be more expensive and time-consuming compared to creating an open source CMS, but in any case, it is the best long-term solution.

4. Skills and expertise: After the development of a custom CMS, clients get a unique ADMIN panel as well as a custom menu that has only the features that are needed to perform the task at hand. This way, people with minimal to almost no computer skills are given the opportunity to work with short stem CMS.

In summary, a Customized CMS is a better choice when an organization has specific and complex requirements, values greater control over the features and security of its website, places a high value on the speed of loading pages from the site, also values UX/UI and has the resources to invest in its development and maintenance for better results.