Some questions, for reasons that are not always entirely clear, attract many "answers" that are not answers. Some of these could be additional questions. Some may be comments on existing answers. Some may simply say "Thanks!" Some may actually be spam (in the strict definition used by Stack Exchange).
When this happens it is often worthwhile to protect the question. Protecting makes it impossible for anyone who has not gained at least 10 reputation on the site itself to post a new answer. The underlying idea is that it is users who are unfamiliar with the site who are posting these non-answers, and to stem the tide we'll prevent them from posting new answers, but still allow the "old guard" to answer.
More information about protected questions can be found in the protected questions Meta Stack Exchange faq, and also the blog post announcing this feature. In particular, from the faq:
- Do protect questions that are attracting a lot of non-answers or very poor answers (spam, etc.) from new users.
- Don’t protect questions just because they’re linked to on a high-traffic news site.
- Do unprotect questions that aren’t currently attracting a lot of attention and don’t have a long history of unproductive answers.
While there is no option to search for protected questions, there are a couple ways to find them.
10K users have access to a Protected Questions list.
The SEDE can find (undeleted) protected questions. For example, this quick and dirty query gives the 100 latest questions to be protected which haven't been since unprotected (modulo the last data dump).