Quality Content is necessary for the search engine and It is most important part for the search engine.If you Content is  good quality then you can easily gain good ranking of your website.
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A hand written unique and informative content is known as quality content, it is a most important part for get high ranking of keyword in search engine result page by giving keywords in content but make sure that never do keyword stuffing in your content, keyword stuffing is against search engine guide lines so to get good result write content by following all search engine guide lines.

Great content doesn't automatically mean great rankings. In other words, it is not a foregone conclusion that great content will necessarily rank just because of its quality. The content may deserve to be ranked, but if no one knows about it, or if the site architecture is so atrocious that it repels the spiders, then it won’t rank. It’s as important to actively promote that great content as to have created it. I’m simply making an argument against that tired old phrase “Build it and they will come.” Don’t let my comments dissuade you from creating high quality content though! Indeed, it’s a likely prerequisite for SEO success, especially when the keywords being targeted are highly competitive.

Well Google is giving priority to fresh and quality content so I think you should keep your content updated regularly for better crawling and rankings in SERP.

Quality is generally referred to as the relevancy in Google's eye.If you have a website for say gift gallery, then the quality content will include the description related to the respective gift items, product etc.,