What is this substance in my canned ground beef?
It's a jelly formed of water and proteins from the meat, primarily collagen.  More or less the same substance as aspic, though &quot;aspic&quot; normally refers to an intentionally created dish of this stuff, rather than a little bit forming as a byproduct of canning.
It's normal for a small amount of this stuff to form naturally at the edges of canned meat products.  It's safe to eat; there's nothing in it that isn't also in the rest of the product.  It will melt down and disappear as you cook the meat.