Hot Network Questions in the right-hand sidebar, the “hot” tab on each site, and on stackexchange.com.
“Hot questions” can refer to two things:
- the list of “Hot Network Questions” in the right sidebar, also available as the “hot” tab of the main Stack Exchange site
- the “hot” tab on each question and answer site
In both cases, questions are included if they hit a large “hotness” in a short time, with hotness determined by score, views and number of answers. The formulas for both cases are different; e.g. questions without answers never appear on the Hot Network Questions, but can appear on a site's "hot" tab.
The "hot" tab of the per-site meta is used to obtain questions to show in the "Hot Meta Posts" block part of the community-bulletin on the main site; for questions about that, use that tag as well.
The network-wide list has further adjustments to avoid being completely dominated by a site, and entire sites can be excluded from the list on a case-by-case basis. Inclusion is fully automatic, and cannot be controlled even by moderators (not without major side effects such as closing the question).
There is no logging of which questions have been included in the past.