What is: Default theme
The theme which is displayed when you install WordPress is called the Default theme. It is basically to show you all the features and functions of WordPress. You can add any theme according to your preferences.
The First theme was created when the WordPress was released in 2003. Users were not given the authority to change themes. After the stable release WordPress 1.5, users were given the authority to switch themes. The Kubrick theme was the default theme at the time of WordPress 1.5. And it was replaced by TwentyTen when WordPress 3.0 was released. Every year since 2010, WordPress releases a new default theme with the year name like TwentyFourteen, TwentyFifteen etc. But TwentyTen is the most famous one.
The default theme though has a lot of features and used to create a basic website. It also helps when a user deletes the installed theme or something gets wrong with the installed theme. You can create your custom WordPress themes using TemplateToaster Software.