What does it mean when an answer is flagged as "very low quality", and what are the common actions a moderator may take when handling this flag?
There are several reasons for flagging answers as "very low quality" (VLQ). They include, but are not limited to:
Severe formatting issues: If a post can be edited by a third party to improve it to the point of not meeting deletion criteria, you should do so if you are able to. Otherwise, you can use the VLQ flag to indicate that the post is not salvageable. The post will be sent to a community review queue, where users can review to delete the post if it is of poor enough quality. They may also comment on the post with the reason for reviewing to delete, in hopes they may edit and undelete (or vote or flag for undeletion). (If the post has already been reviewed in the queue, the flag will be sent to moderators instead.)
Incomprehensibility: It may be an answer, but it's so bad that it could never be saved through editing.
Other severe content problems: This includes answers that don't attempt to answer the question (which can equivilently be flagged as "not an answer") and answers devoid of content (such as "try jQuery!").
However, the "very low quality" flag should not be applied to an answer if:
The answer is just incorrect. It is not the job of moderators to deal with answers that are incorrect in some respect. Users should downvote wrong answers and (optionally) leave comments that describe why they are wrong. The answerer would, in the best case, update the answer to fix whatever issues it has, or delete it. We even have a badge for that.
It is spam or abusive. Spam and abuse flags are handled differently and carry higher penalties. If a post meets the criteria for one of these flags, you should flag it as such rather than Very Low Quality.
Moderators should dismiss a "very low quality" flag on an answer that is technically incorrect. The moderator may take into account the quality of the answer when deciding to mark the flag as "helpful" or as declined for one of the standard reasons.