At its core, WordPress is a content management system (CMS) that enables you to create a website or blog from scratch, or to improve an existing website. WordPress is free and open source software released under the GPL, making it an attractive option for those looking for a platform to create a website or blog on.
There are many different themes available for WordPress, each designed to give you a unique and customized experience when creating and managing your website or blog. Some of the more popular themes include Twenty Fifteen, Genesis, and bbpress.
However, there are also many unique and niche themes available, perfect for those looking for something specific.
Ultimately, the most basic WordPress theme is the one that you choose to use. However, if you are looking for a specific type of theme, or if you want to customize your WordPress experience in other ways, there are many available options.
So, whether you are looking for a basic or advanced theme, there is likely a suitable option available for you.