I recently came across the term "voluntary long-term disability insurance." I certainly know what disability insurance is, but I've never heard the word "voluntary" attached to it. Wondering if this means it's a different type of disability insurance, I googled around and found the term is actually fairly common and gets applied to other types of insurance as well. Here is an example.
However, I've been unable to find an explanation of this term, what's voluntary about it, and what it means exactly. So my question is:
What is voluntary disability insurance and is it different from disability insurance? And if there is no difference, why is that word sometimes applied?