Hmm, I though it was the same. If not, I could imagine a broken link links to a page that returns HTTP code 500, 503, maybe.
And a dead link returns HTTP code 404.
Both are same. Atleast Wikipedia thinks so
"A link that no longer points to its target, often called a broken or dead link, is a specific form of dangling pointer."
So does many other SEO sites
Planzer