Quality content is, when you are writing an article (or) press release you have to write the content as your own. You don't copy the content from other websites (or) from blogs. The Content must be very unique and fresh and that must be understandable by User.
Don't go that "quality content when doing SEO" route. Quality content is something that your potential audience might want to read, and that you can somehow turn to profit. Of course you don't want to post duplicate articles, but that's not usually a problem unless the content you're trying to use is of questionable quality.
The content that your are going to produce should and will attract the audience that will ultimately buy something from you. Whether you’re a product developer or a service provider, content is what’s going to show people that you have both the knowledge and skills to help them.
The content you have created targeting your audience which brings great value to the user. A awesome content is able to force user to be engaged for a long time. Obviously your content should be unique as well as captivating.
The content which is not spammy or duplicate is said Quality content.
Many people post there same article and blog to several different sites, this is wrong, one should not do that. Always use fresh contents for your site.