What can cause a question to be "bumped" to the first page in the Active tab of a Stack Exchange site?
The following will cause a question to be bumped:
The following will not cause a question to be bumped:
* This holds true for edits that generate a revision in the post history. Edits on a post within 5 minutes of its creation or another revision-generating edit fold the changes back into the previous revision, and do not cause the post to be bumped
**Questions with sufficiently low score will not be bumped when either they or their answers are edited. The "sufficiently low" threshold is -4 on SO and new SE sites, and -8 on MetaSO (as of Aug 25, '10 -- see Grace Note's comment).