Direct traffic in Google Analytics can be from multiple types of sources, but it can be defined as the traffic coming to a site by directly typing your site URL or clicked from the bookmark bar.
Sometimes the direct traffic is so high that it is difficult to decide if a such number of people bookmarked or remember your site url. To explain this further, let’s look at the image below:
As you can see in the above image, new sessions and new users can not be so high. If the direct traffic is what people are typing the url then why they are showing up as new users? Don’t you think that a user once visited your site is identified as a returning user in the next visit?
You should know the fact that there are thousands of traffic sources, and GA tries to present accurate traffic as much as it can. Anything that GA couldn’t decide the actual source, it puts it under the direct traffic.