What does active mean?

Question

In any post there are three attributes:

1. Asked
2. Viewed
3. Active

What is the meaning of the active in a post?

Answer 1

"Active" shows when the post was last active. Active means that it has a change: an edit, an answer, an edit to an answer, bumped by Community♦ etc...

It might happen that the "last activity indicator" displays an activity which is nowhere to be seen. This can be the result of:

• an answer which has been deleted since then (spam/rude/not an answer etc);
• a bounty being set up;
• a closed question being reopened (last activity then reads modified by whoeverCastedLastReopenVote);
• the Community♦ user bumping the question so that its answer can be peer reviewed/accepted.

New comments don't make a question "active".

Answer 2

Adding some more/official info on top of ProgramFOX's great existing answer.

We explicitly update the LastActivityDate during the following operations:

• When a post is edited^†
  • When an answer is edited, the question it's associated with will also have have the activity date updated.
  • This includes tag only edits on questions
  • ^† Except in cases we're we've explicitly suppressed edits. These cases are manually set when doing large dev-only updates, like batch tag renames or url rewrites.
• When a new answer is added to a question
• When a question is re-opened
• When a question is bumped by the community user
• When a bounty is started on a question
• When a post is rolled back, the LastActivityDate is set to the current time (when the rollback occurred)
• When an answer is moved if the answer date is more recent than the new target question last activity date
• During post migration
  • the LastActivityDate is preserved for answers.
  • we may retain the LastActivityDate or use the migration date for questions, depending on how the migration was invoked.

Last active date is NOT updated when:

• A question is closed
• A comment is added to a post
• A post is deleted or undeleted
• A post is voted up/down
• A question has an answer accepted
• A bounty is awarded to an answer
• A mod protects or unprotects a post
• A mod adds a post notice

You can easily check the last active date for a question at the top of page on the post summary

If you want to double check the value for answers (or for questions), the last activity date is available in SEDE

Additional Notes

• In terms of the actual language, we changed from the word active to modified back in 2022
• There are occasionally edge cases where an answer is added and updates the last activity date, but is subsequently deleted, which can make it hard for users without enough rep to piece together what the new activity was.
• This value is also used in the sort on ?tab=Active
• We store LastActivityDate property set on each post in SQL Server and also kept up to date in elastic for searches.