user3650: I was recently reviewing a new users first post when I noticed this....

This is a new user's answer to an old question. Watch for hidden gems, non-answers, and spam. 

I've seen this notification/banner a hundred times and not once did I think about the words "Hidden Gems" until now. So what are they?
Heres what the banner looks like.

Answers are appreciated. :)

user274: According to the Stack Exchange glossary, this is the definition of a hidden gem:

This term refers to a post that is surprisingly outstanding in quality, especially coming from a new user. Those are hard to find and rare, so keep your eyes open!

Basically, when a question is left abandoned for a while and then answered later (a month or more), or by a new user, that answer may not get noticed, particularly if the OP doesn't frequent the site. So, even a very good answer might get no upvotes or recognition, which does against the Stack Exchange ideal.
So in the review queue, make sure to upvote and bring attention to posts like this!

3650: <p>I was recently reviewing a new users first post when I noticed this....</p>

<blockquote>
  <p>This is a new user's answer to an old question. Watch for hidden gems, non-answers, and spam. </p>
</blockquote>

<p>I've seen this notification/banner a hundred times and not once did I think about the words "Hidden Gems" until now. So what are they?</p>

<p>Heres what the banner looks like.</p>

<p><img src="https://i.stack.imgur.com/l7gGb.jpg" alt="enter image description here"></p>

<p>Answers are appreciated. :)</p>
 274: <p>According to <a href="https://meta.stackexchange.com/a/40354">the Stack Exchange glossary</a>, this is the definition of a hidden gem:</p>

<blockquote>
  <p>This term refers to a post that is surprisingly outstanding in quality, especially coming from a new user. Those are hard to find and rare, so keep your eyes open!</p>
</blockquote>

<p>Basically, when a question is left abandoned for a while and then answered later (a month or more), or by a new user, that answer may not get noticed, particularly if the OP doesn't frequent the site. So, even a <em>very good</em> answer might get no upvotes or recognition, which does against the Stack Exchange ideal.</p>

<p>So in the review queue, make sure to upvote and bring attention to posts like this!</p>
