Seedfork is exactly right. A jiffy is 1% of a second (meaning, it takes 100 jiffies to make a second) and the number appears because it's telling you how long it took the server to generate that page.
ATP is actually a software program. Each page is created automatically by the software and it takes computational resources to generate those pages. Particularly heavy pages get the timer so I can monitor if a page is taking too long to load.
