As per other answers, slug is stored in the `post_name` property. While it _could_ be accessed directly, I prefer the (underused) `get_post_field()` function for accessing post properties which have no proper API for them.

It requires post provided explicitly and doesn't default to the current one, so in full for the current post it would be:

    $slug = get_post_field( 'post_name', get_post() );