Ardour allows arbitrary layering of regions — you can have as many regions you wish at a given position. By default, the regions are overlaid in the editor window, to save vertical space.
However, this display mode can be confusing for tracks with many overdubs, because its not obvious in which order the overdubs are layered. Although there are other methods of moving particular regions to the top of an overlapping set, and although Ardour also has playlists to let you manage takes a bit more efficiently than just continually layering, there are times when being able to clearly see all regions in a track without any overlaps is reassuring and useful.
Here is an image of a track with a rather drastic overdub situation, viewed in normal overlaid mode:
To change this display, right click on the track header, and you'll see the menu displayed above. There are two choices for layers. overlaid is currently selected. Click on stacked and the track display changes to this:
You can still move regions around as usual, and in fact you can even drag them so that they overlay each again, but when you release the mouse button, things will flip back to them all being stacked cleanly. The number of lanes for the track is determined by the maximum number of regions existing in any one spot throughout the track, so if you have really stacked up 10 overdubs in one spot, you'll end up with 10 lanes. Obviously, using a large track height works much better for this than a small one.