Say you have this thread open in Safari on your iPad. You want open the iOS thread list from the breadcrumb links at the top of the page in a new tab. But the link that says iOS is too small so your option is to either click and hold to get the list to open in new tab or you place your fingers above and under the link like this:
(==== <-- finger
iOS
(====
Then tap with those fingers. The link between your fingers will open in a new tab.
I think how it technically works is that the software draws an area between the two touch points and whatever intersects that area is the desired link.