Both.

From http://wordnet.princeton.edu/perl/webwn?s=lie

<quote>
(n) lie, prevarication (a statement that deviates from or perverts the
truth)
[...]
(v) lie (tell an untruth; pretend with intent to deceive)
</quote>

The first definition quoted here says nothing about intent; that is, a
statement is defined to be a lie depending on whether it is true or not, as
opposed to whether the speaker intended for that statement to be true or
not.

The second definition could arguably be split into two parts, showing that
lie has two meanings. One is to make a statement which is not true, and the
other is to intentionally deceive.

If you used the above definitions as the Final Authority on English, you
might pedantically argue the case that when "lie" is used as a verb, it
always implies intent to deceive (and thus argue that the semicolon does NOT
split the definition into two meanings, but rather the second part
supplements the first), whereas when used as a noun, it conveys no
information about intent.

However, I've found it useful to simply accept the fact that when some
people use the word "lie", sometimes they aren't saying anything about
intent, but merely about the truth value of the statement being described. I
find that there is a large enough number of these people that it's not worth
trying to "correct" their usage, and just accept this new meaning as a
natural evolution of the English language.

So when you get into a debate with someone, and they use the term "lie", you
might want to get clarification on what they mean by that term, and then you
can discuss whether another term might be more appropriate, or just agree to
use the agreed upon definition for the purpose of that particular debate,
and perhaps later on in another debate, with a different person, agree on a
different definition.

   - Oliver