A link without a text alternative is basically an empty <a> tag. They are usually created by adding a new link but not completing it, or deleting the text in a link without unlinking it first.
The easiest way to identify these errors is to look in the source code for <a> tags without any text between the brackets:
<a href="/about/index"></a>
A normal link will look like this:
<a href="/about/index">Learn more about us.</a>
There are seveal links in the dummy copy below that are missing a text alternative.
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Proin luctus nisi ac metus faucibus accumsan. Pellentesque sed velit quam. Donec a tempor nulla, sed blandit nibh. Donec vitae consectetur odio, sit amet iaculis erat. Suspendisse faucibus eros id tempor tincidunt. Phasellus tempus fermentum tincidunt. Proin maximus posuere risus vitae mattis. Donec feugiat, purus ac ornare scelerisque, nibh orci bibendum metus, a imperdiet ex eros vel velit. Maecenas turpis leo, finibus sed velit ut, ullamcorper gravida libero. Nunc feugiat risus libero, sed egestas lectus mattis congue. Praesent consectetur maximus est, nec dictum lectus placerat in. Vestibulum consectetur diam sed consectetur pretium.
Morbi blandit ut nisi non aliquam. Phasellus dictum diam sit amet ligula venenatis, id varius nisi dictum. Quisque facilisis ligula id sapien mattis, ut accumsan felis porttitor. Nam turpis mi, blandit ut rhoncus vel, elementum quis velit. Nunc ullamcorper fringilla pretium. Curabitur sed dui nunc. Vivamus pulvinar est nec laoreet elementum.