So, if I'm reading you right, you're talking about the depth-of-field scales printed on lenses, like the ones on this image:
If that's not what you're referring to, ignore the rest of what I say. The center line just below the distance scale shows where the lens is focused (about 1.6 meters in this case). To the sides of the focus line are marked the ranges that will be reasonably in focus when you set various apertures. As the lens is set now at f/11, anything from about 1 meter to about 2 meters (~3-6 feet) will be reasonably in focus. To the left of the lens, the dot shows where to focus for infrared photography. Glass bends low energy light (like infrareds and reds) less than it bends high energy light (like blues and violets). Incidentally, the fact that different color light gets bent differently is why you have so many elements even in prime lenses--having different focal planes for different colors (chromatic aberration) isn't really an effect photographers go for, for obvious reasons. (Although some do buy single-element lensbabies.)
The marks to the left of that center line are also called hyperfocal marks. If you've heard people talk about focusing at the hyperfocal distance (and you will have if you've heard a landscape photographer talk much), it's when you focus at a point a bit closer than infinity to get the biggest range of the frame in focus. If you set the focus at infinity, you waste some of it because the range of in-focus distances extends beyond infinity (whatever that means), but if you line up infinity with the hyperfocal mark for the aperture that you've set, you get the maximum range of distances in the frame in focus.