What does "barely" imply?

Question

When someone says,

I barely understand that.

Does he mean:

1. He almost doesn't understand [which means he understands a bit]
2. He almost understands [which means he doesn't understand]

Or if someone says:

Your brain is barely used.

Does he mean:

1. Your brain is almost not used [which means, it is used, but very rarely]
2. Your brain is almost used [which means it isn't]

I used to think that it was the first option. But a friend, out of the blue, said it was the second one.

Which one is it? Or have my friend and I got it entirely wrong?

Are there other words with similar meanings to barely? Is nearly one of them?

Answer 1

It is item 1 in your post in each case which is correct.

It would be used to stress the fact of 'how little'. E.g., 'How can I possibly agree to marry him, I barely know him !'