It's very common to see the usage of the tag <nav>
in a main menu navigation, but I don't know other examples where I can use it. For example, for pagination:
<div class='my-pagination'>
<!-- first, 2, 3, 4 ... 8, 9, last -->
</div>
Can be:
<nav class='my-pagination'>
<!-- first, 2, 3, 4 ... 8, 9, last -->
</nav>
Is it semantic?