Directory Submission is an off-page SEO Optimization activity work. Its submission of your blog and site to a related a specific category of a web directory, e.g if you have a business blog and website then you are supposed to submit your site in the business category of a web directory. Directory submission work as a like phone directory. Directory submission is available in the market now free and paid.

Note: But the last few years, directory submission work for not longer benefits thousand of links to your blog so you can game Google. Now Time directory submission is useful if we use a carefully and relevant way.