Question about new posts feature

[Ron V]

Just curious about something. I like to use the new posts search as I generally visit the forums each day at about the same time. I was wondering what makes posts new? If that doesn't make sense , I'm referring to the fact that sometimes there are 20 or more new posts , and sometimes only a few , or none. Is this just because there ARE much fewer posts on a certain day? It seems weird that on a site with this many subscribers that there are days when so few of us post. Or is it because the new posts are determined by being X number of hours old? Thanks , just wondering...