Copywriting is a form of communication. It is simply the writing of words to inform, persuade etc.
A "copywriter" coined back in the early 1900s after the term "copy-boy" was used, may be employed by advertising agencies and public relations firms. The word "copywriting" may be most prevalent in the marketing industry. Professional copywriters can make well into the 6-figure salary range if they understand how to craft a piece of content that at the end of the day drives views, or sales.
This may be crafting a click-worthy headline, writing an article that sways the reader to make a buying decision, or scribing an audience-captivation political speech.
Search engine optimization (SEO) is the process of affecting the visibility of a website or a web page in a search engine's unpaid search results-often referred to as "natural", "organic", or "earned" results. In general, the earlier (or higher ranked on the search result page), and more frequently a site appears in the search results list, the more visitors it will receive from the search engine's users; these visitors can then be converted into customers.
A strong relationship lies between the art of writing copy, and ranking well on search engines.
Not only do humans read the copy on a webpage, but search engine crawlers do as well. There are little "bots" that crawl the web on behalf of search engines. They report back to the database the content on each webpage, conveying to engines like Google which pages are most relevant, and which results would be the ideal search result when responding to a user's search query.
Because the copy on each webpage determines how search engines display those pages, copywriting plays a large role in search engine optimization.
It's important for copywriters to always keep in mind what keywords they are trying to rank for (which is the practice of keyword research), and the fact that including those keywords not only throughout their content, but in specific locations in their content can help them achieve this goal.
The title tag of a webpage is the most prevalent text displayed in search (the blue link), and should be treated similar to an H1 when deciding how to structure them.
Search engines will put more value on headers (in order of H1-H6) than the rest of the body on the page. This is because they believe (and rightly so) that they are used to navigate the reader through the content. So being very aware of how you include primary keywords and supporting keywords in your page headers can make or break your SERP placement.
The right density is about 1-3% of the words in the article. This is about how often it would appear in your text if you were writing about the topic without the intention to over-use the keyword. In short, use it where it makes sense, and don't where it doesn't. Google will be able to understand the content of the article without overuse of the keyword(s).
Effective copywriting can (and most certainly will), determine SERP ranking, and ultimately effectiveness of your SEO campaigns in general. By utilizing keywords the correct way in the copy of the page, and by reverse-engineering a high reader-time spent on page, the right copywriting can help the bottom line of your business, attracting more traffic, and closing more sales.