Each block has a name (defined by < block ... name="block_name" > in layout xml)
and most blocks have a child alias (defined by < block ... as="child_name" > in layout xml)
is used to simplify templates and make use of the layouts.
From your request it looks like you don’t really care about layouts structure.
In your case I would use just block name which is accessible from any template:
Which might be reduced to:
in future releases.