The primary reason why SSL is used is to keep sensitive information sent across the Internet encrypted so that only the intended recipient can access it.

The title tag on each page tells both users and search engines what the page is about.

 A backlink is created when a page of another website links to a page on yours. Backlinks are important to search engines because they are a signal that the site being linked to has quality, worthwhile information on a topic relevant to the site linking to it. You can think of it as a digital vote of confidence.

Hidden texts is consider as search engine spamming to get higher rank on SERP. It is also called as Black Hat SEO techniques.

Keyword Difficulty is the measurement criteria to know how much a keyword is difficult to rank for.