A properly presented, well articulated, easy to understand, meaningful and credible content in a post is what quality means to me.

The key word here is meaningful. If it is well articulated, grammatically correct and easy to comprehend with explanations for any technical jargon used then it's easier to make out what the post has to offer to me. If the post is authoritative, logical, with all the required credible references then it looks trustworthy and hence qualitative to me. If the post has good formatting and appealing to my eyes, it is inviting to me and is easier to read through. This imparts a good reputation to the content creator and hence the content as well, so it become more meaningful to me.