You can pay for advertisements on social media platform (Facebook, Instagram…) or on Google. When people see them and click on them, they are taken to your website. Those visitors to your website are called paid traffic. But people can visit your website another way. They open Google (or another search engine) and type in what they’re looking for. Google serves them results it thinks are the most suitable. If your page is listed there (SERP) and people click it, they visit your website. That is called organic traffic. Good SEO will get you high on that list Google makes.