By default, WordPress comes bundled with a category called Uncategorized. It acts as a fallback category. WordPress assigns this category to a post at the time it is published, if no other category is selected. In other words, it is the default category for WordPress.
If you want to change default category from Uncategorized, to something else, you can do that using Default Post Category option from Dashboard.
To Change the Default Category follow the steps given below,
1. Login to your Dashboard.
2. Navigate to Settings >> Writing
3. Look for Default Post Category option.
4. From the dropdown menu, select a new category and hit the Save Changes button.