Traffic is mainly the number of visitors a website receives. The truth is : traffic is everything. More than readership, it is traffic that makes you money. Loyal readers are cool to have and are certainly people who buy your courses, books, etc. But before they are readers, they are nothing but numbers on your Google Analytics dashboard. No matter what your blog is about, no matter if it is even a blog or even if you have 1000s of posts, if you have nobody to see those posts, you have nothing. It might offend some people, but the fact is fact.
Call me a generalization-wizard, but what do you got if you got no traffic to boast of? Who buys your courses? Who clicks your ads? Who reads what you write? Who subscribes to your blog? Yes, subscribers, customers, readers, etc. are most basically traffic. And have more to do with success of any blog.