The aurochs is proud and has great horns;
it is a very savage beast and fights with its horns;
a great ranger of the moors, it is a creature of mettle.
For the rune Ur, I have again quoted the Anglo-Saxon rune poem, a translation of which can be found here. The Norwegian and Icelandic poems are debatable, but I personally do not associate the second stanzas of those poems with this Rune.
I have always seen this rune, in a Elder Futhark context, represented as Strength. Which is fair - the aurochs is incredibly large and strong. But that's not exactly what the poem is saying. It talks about the pride of the aurochs, it's bravery. Now of course, the aurochs can be brave and prideful because of its great strength; it has the power to back up its claims. In fact, it is a savage beast, and will prove its power beyond a shadow of a doubt with sufficient provocation (and reading about aurochs, it seems like 'sufficient provocation' could have been pretty minimal!). This rune makes claims of strength because it has that strength, and will not hesitate to show it off when confronted.