how do old threads keep popping up to the top of the list?

[upgrading mama]

This may be a dumb question, but i have noticed that some old threads keep returning to the top of the list? is it bc someone new has added a post?

 

[glaucomflecken]

when you post to any thread it "bumps" the thread up to the top of the list again!

 

[upgrading mama]

thanks, good to know!!!